Real-time updates in lobby

[scott-coates]

Description

Ensure all changes are reflected in realtime for each player.

Requirements

• New players should show up in realtime. The current user should always be at the top of the list of players with the suffix (You).
• Changing the category should be reflected on every player's screen.
• The start game button is disabled until at least 2 players join the lobby.
• Remember, only the game creator (host) can make changes and start the game.