Touched up how the CameraManager and SceneManager interoperate during startup and shutdown.  Also did some minor code cleanup.
Did some code cleanup to the Camera class, although I'm not sure why considering it will be purged.
Added a CameraProxy enum value to the enum for world proxies.
Documentation fixes.
I believe I have finished the non-serialization code of the CameraProxy.
Implemented serialization for the CameraProxy.
Purged the old Camera.  Put CameraProxy in it's place.
Merge branch 'master' of https://github.com/BlackToppStudios/Mezzanine