Two hooks for DoctrineBundle to allow ContainerFilterCollection

Allows the DoctrineBundle to inject a ```ContainerFilterCollection``` that creates filters through dependency injection. See doctrine/DoctrineBundle#245.

Would prefer to inject the ```FilterCollection``` into the constructor of the em, but since they have a cyclic dependency I chose setter injection.
This code was only moved from ```FilterCollection->enable()```. Wouldn't throwing a different kind of exception be a BC break?