Fix EZP-22279: Integrate storage engine configuration with DoctrineBundle connections

https://jira.ez.no/browse/EZP-22279

Depends on https://github.com/ezsystems/ezpublish-community/pull/113

This PR adds native support of DoctrineBundle, for DBAL configuration (ORM **not included**).

Added notion of *repository* in the configuration.
Repositories are declared globally and used/specified at the SiteAccess level (or group).

A repository consists of an *engine* (to specify which storage engine to use), and config options for that engine.
In the case of `legacy`, aka LegacyStorageEngine, a Doctrine *connection* is specified, which is configured in DoctrineBundle.

Example of semantic configuration:

```yaml
# Using Doctrine default connection
doctrine:
    dbal:
        driver:   pdo_mysql
        host:     localhost
        port:     3306
        dbname:   ezdemo
        user:     root
        password: root
        charset:  UTF8
 
ezpublish:
    repositories:
        # Takes all default values (engine: legacy, connection: default)
        main: ~
 
    system:
        ezdemo_group:
            # Optional, if not provided, will take the first defined repository by default
            repository: main
 
#####
 
# Using a named Doctrine connection
doctrine:
    dbal:
        default_connection:       default
        connections:
            default:
                dbname:           Symfony2
                user:             root
                password:         null
                host:             localhost
            my_connection:
                dbname:           customer
                user:             root
                password:         null
                host:             localhost
 
ezpublish:
    repositories:
        main:
            # legacy => Legacy storage engine
            engine: legacy
            connection: my_connection
```

## BC Break
A BC break has been introduced in database configuration. `ezpublish.system.<siteaccess_name>.database` setting is no longer supported (see `changes-5.3.md`).
However, a new *configuration suggestion* mechanism has been introduced to give hints on which settings to change:

![configuration_suggestion](https://f.cloud.github.com/assets/313528/2196491/421e2754-98b0-11e3-9fb2-278999904b16.png)

> Note: The same message is also readable in web view.

## TODO
* [x] Refactor factories to use Doctrine connections
* [x] Implement semantic configuration
* [x] Fix existing tests
* [x] Add new tests
* [x] Add documentation
* [ ] Update config dumper (for setup wizard)