CurrentMembers as functional component

[exidy80]

Same 'presentMembers' algorithm, but without the chance of an infinite loop. If this doesn't behave as we'd like, we can go back to the other algorithm for figuring out presentMembers.

However, we really should address some deeper bugs, such as:

• "members" containing repeats of people occassionally
• the need to filter malformed users
• the "current in room" number in the lobby is often not accurate when you exit a room.