Allow room to remain open after both player disconnect
Currently the room will remain open if one player disconnects. When a second player reconnects it will resync them and the game can continue.
If both players are playing on mobile devices, it's likely that both websockets disconnect even though both players are still playing. This currently causes the room to die and the game to end.
This should be fixed so that the room can remain open for some amount of time even if both players disconnect. The server will also need a way to reassign the player to the correct mark when they reconnect. When only one player could disconnect this was not a problem, but if both players disconnect we need a way to correctly reassign marks.