gameplay: remove LOGIN/LOGOUT, just search for MM
refactoring: move game logic into new "shared" module so we can use it in the game server; move Model Instance code out of GameTile and into GameGraphics

I'm still not happy with the way I'm attaching the ModelInstance to the GameTile (get/set nativeHandle), but it'll do. Might want to make an ABC/interface if we have many more objects that need to be serialized and also hold graphical handles