Morph ManagedActor into Scene

[devpow112]

Currently we have a stand alone set of functions for managing what we call ManagedActors. Although this is useful for overall life-cycle management, it doesn't help with categorizing actors into groups for things such as collisions. This knowledge is more the place of a scene manager. Add a Scene set of functions for managing a grouping of Actors while allowing for categorization and life-cycle management. Make sure to keep soft resets in mind in terms of auto clean-up of actors/scene stuff.