- Removed MeshCreationCommand and PrimitiveMeshCreationCommand classes.
- Now ClientPrimitivesManager depends on DrawablesManager and MaterialsManager instead of the contrary.
	- Now the user "instantiates a primitive" instead of "creating a mesh from a primitive".
- Added a new PrimitiveInstantiationCommand class.
- TODO: Read materials from primitive files.
- TODO: Sync the instantiation of primitives in other clients.