[#23] lobby's update doesn't use allClientIds to represent clients
* lobbyClientIds is a filter of allClientIds & playingClientIds
* need to run update/clientConfirmation when beginGame fires
* also, need to get clients to ignore update lobby events once they
are in a room. maybe i need to make a lobby room?! fish.
[#24] join clients to 'lobby' room on socket connection
* TODO: refactor getLobbyClients()
* TODO: rename emitClientConfirmation()