Implemented turn-taking.
Created ADD_PLAYER, SETUP_DONE, NEXT_TURN PacketMessage types.
ADD_PLAYER used for adding Players to a match.
SETUP_DONE signals the server is done with setup and ready for gameplay.
NEXT_TURN signals the current player is done with their turn.
Cleaned up some hidden bugs dealing with playerIDs
Only show playerID in Entity Info Panel if playerID != 0