AnimationFactory now keeps track of the various Animation pointers.
Actor doesn't have to, anymore. This simplifies the code a bit.
Referenceable: now it can delete automatically the items if false is passed
on the constructor. The default behaviour is not to delete them automatically.
Use this feature to handle AnimationFactory lifetime. Now Actor
releases AnimationFactories in the destructor.
Note that we don't yet delete Actors (std::vector::erase() doesn't call
destructors)
Wrong check
Fix compilation
Release the AnimationFactory
Don't use std::vector::erase because it doesn't call destructors