[DoctrineORMMapper] added Discriminator, Discriminator Column, and Inheritance Type.

You can now extend the inheritance of another class.

example:
```php


        DoctrineCollector::getInstance()->addDiscriminator(
          '\Acme\AcmeDemoBundle\Entity',
          "MY",
          '\Acme\AcmeDemoBundle\MyEntity');

        DoctrineCollector::getInstance()->addDiscriminatorColumn(
          '\Acme\AcmeDemoBundle\Entity',
            array("name"=>"discr", "type"=>"string")
        );

        DoctrineCollector::getInstance()->addInheritanceType(
          '\Acme\AcmeDemoBundle\Entity',
            \Doctrine\ORM\Mapping\ClassMetadataInfo::INHERITANCE_TYPE_JOINED
        );

```