Declared some C++ objects as private since they are not directly interacted with.  This includes classes that have a singleton instance as well as classes that are only exposed as an inherited class of another class.

Renamed GameEngine to EngineServer to match the name of the singleton to its class _EngineServer.  The same goes for Globals which is now GlobalVars.

Renamed a few engine module file names to use engine_ instead of eiface_.