Ensure element link exist
Ensure element link exist

The form type media_type can be manipulated with events, inherits etc 
Now we can remove element unlink without have 
Child "unlink" does not exist. - 500 Internal Server Error - OutOfBoundsException
Soullivaneuh/SonataMediaBundle,jerome-fix/SonataMediaBundle,vyshkant/SonataMediaBundle,vyshkant/SonataMediaBundle,hug963/SonataMediaBundle,hug963/SonataMediaBundle,bgaleotti/SonataMediaBundle,jerome-fix/SonataMediaBundle,nicolasricci/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,OskarStark/SonataMediaBundle,OskarStark/SonataMediaBundle,nicolasricci/SonataMediaBundle,sonata-project/SonataMediaBundle,bgaleotti/SonataMediaBundle,vyshkant/SonataMediaBundle,jerome-fix/SonataMediaBundle,hug963/SonataMediaBundle,OskarStark/SonataMediaBundle,vyshkant/SonataMediaBundle,bgaleotti/SonataMediaBundle,OskarStark/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,bgaleotti/SonataMediaBundle,hug963/SonataMediaBundle,nicolasricci/SonataMediaBundle,jerome-fix/SonataMediaBundle,nicolasricci/SonataMediaBundle,nicolasricci/SonataMediaBundle,vyshkant/SonataMediaBundle,Soullivaneuh/SonataMediaBundle,hug963/SonataMediaBundle