[DDC-3205] Metadata info

This PR adds support for showing the metadata for a single entity to the `orm:info` command.

- The original behavior is preserved (running without arguments validates and lists all the entity names)
- The output is formatted using the `TableHelper` if it is available (Symfony 2.4+). If the TableHelper is not available
it will format simply with `field: value`.
- Partial regex matches are accepted, e.g. `mapping:info Attraction`, `mapping:info Attraction.*`

E.g.:

````bash
$ php app/console doctrine:mapping:info "Sulu\Bundle\ContactBundle\Entity\Count"
+-------------------------------+-----------------------------------------------------------------------------------------------+
| Field                         | Value                                                                                         |
+-------------------------------+-----------------------------------------------------------------------------------------------+
| Name                          | Sulu\Bundle\TagBundle\Entity\Tag                                                              |
| Root entity name              | Sulu\Bundle\TagBundle\Entity\Tag                                                              |
| Custom generator definition   | None                                                                                          |
| Custom repository class       | Sulu\Bundle\TagBundle\Entity\TagRepository                                                    |
| Mapped super class?           | Empty                                                                                         |
| Embedded class?               | Empty                                                                                         |
| Parent classes                | Empty                                                                                         |
| Sub classes                   | Empty                                                                                         |
| Embedded classes              | Empty                                                                                         |
| Named queries                 | Empty                                                                                         |
| Named native queries          | Empty                                                                                         |
| SQL result set mappings       | Empty                                                                                         |
| Identifier                    | ["id"]                                                                                        |
| Inheritance type              | 1                                                                                             |
| Discriminator column          | None                                                                                          |
| Discriminator value           | None                                                                                          |
| Discriminator map             | Empty                                                                                         |
| Generator type                | 4                                                                                             |
| Table                         | {"name":"ta_tags"}                                                                            |
| Composite identifier?         | Empty                                                                                         |
| Foreign identifier?           | Empty                                                                                         |
| Sequence generator definition | None                                                                                          |
| Table generator definition    | None                                                                                          |
| Change tracking policy        | 1                                                                                             |
| Versioned?                    | None                                                                                          |
| Version field                 | None                                                                                          |
| Read only?                    | Empty                                                                                         |
| Entity listeners              | Empty                                                                                         |
| Association mappings:         |                                                                                               |
|   creator                     |                                                                                               |
|     fieldName                 | creator                                                                                       |
|     targetEntity              | Sulu\Bundle\SecurityBundle\Entity\User                                                        |
|     joinColumns               | [{"name":"idUsersCreator","referencedColumnName":"id","nullable":true,"onDelete":"SET NULL"}] |
|     type                      | 2                                                                                             |
|     mappedBy                  | Null                                                                                          |
|     inversedBy                | Null                                                                                          |
|     isOwningSide              | 1                                                                                             |
|     sourceEntity              | Sulu\Bundle\TagBundle\Entity\Tag                                                              |
|     fetch                     | 2                                                                                             |
|     cascade                   | Empty                                                                                         |
|     isCascadeRemove           | Empty                                                                                         |
|     isCascadePersist          | Empty                                                                                         |
|     isCascadeRefresh          | Empty                                                                                         |
|     isCascadeMerge            | Empty                                                                                         |
|     isCascadeDetach           | Empty                                                                                         |
|     sourceToTargetKeyColumns  | {"idUsersCreator":"id"}                                                                       |
|     joinColumnFieldNames      | {"idUsersCreator":"idUsersCreator"}                                                           |
|     targetToSourceKeyColumns  | {"id":"idUsersCreator"}                                                                       |
|     orphanRemoval             | Empty                                                                                         |
| Field mappings:               |                                                                                               |
|   name                        |                                                                                               |
|     fieldName                 | name                                                                                          |
|     type                      | string                                                                                        |
|     columnName                | name                                                                                          |
|     unique                    | 1                                                                                             |
|   created                     |                                                                                               |
|     fieldName                 | created                                                                                       |
|     type                      | datetime                                                                                      |
|     columnName                | created                                                                                       |
+-------------------------------+-----------------------------------------------------------------------------------------------+

nope. It just yell at you if there is an exception in the metadat loading. Part of the mistakes in the mapping are not throwing exceptions when loading the metadata (which is why there is a validator class used by the dedicated command.

It does not give more validation than any other command using some mapping info (except you rendered the exception yourself instead of letting the Application class do it)