Add TODO
Nicen up player list
Moving pixels
Better function order
Always log errors
Include possible edge-case in error handling

It may happen that the error passed to `panic` is nil but of type
error. This is most likely a programming error so it should be logged
as well.
Only report when there's an actual error
Regard special case in game handler

There may be an invalid session in which case the player is prompted
to sign in as a user to join the game for convenience.