Scene makes no sense. Kill in favour of Space

[ikeycode]

Literally it serves no purpose right now. We don't have a scene graph and kinda don't want one either.

Rather, we would prefer some notion of a Space, which has its own set of entities. This would allow us to hotswitch between two complete system states by updating which set of entities we have access to.

This would require storing a list of spaces within the EntityManager, each with their own independent storage buckets. The StagingArchetype and manifest would need to come from the parent EntityManager and a clear() operation would need to nuke all spaces. However each Space should also support a clear() too...

[ikeycode]

Many APIs would remain unchanged, and we could add a nice context.entity.space = API to dynamically switch the set of entities we engage with. We'll need this to permit GUI screens and level/room switching in the RPG demo.