prevents registering while server User has games in progress and moves _isLoggedIn
check outside the database callback
adds Event require to server Game
adds id to server User.toJSON so that the client can compare anonymous users
adds _id, getId() and HasIdentity event to client User so that client code can
update the ui when the user knows its id on the server
adds getUserColour to client Game to check whether the user is a player in the game, and which colour