A bit of an architectural change before we progress further. Moved
player code into a shared PlayerBass class to elimnate some severe code
duplication while i was getting things working.
* Added Player class to represent players on the server.
* Added Game class to manage the overall game state.
* Server now adds new players to the game state when they connect.
* Server now updates the players position in the game state on receiving
a PlayerPosMessage.