Add cmd_presence

[alexalok]

Add a new terminal command to allow presence in a specified global room (with the possibility of addition and removing).

[Levak]

Interesting idea.

I drop some design questions here:

• Should it be able to join the clan room?
• How would cmd_say behave after joining multiple rooms? For instance, one game room, 2 global rooms, and the clan room.
• Wouldn't it be easier to automatically join global room as the game does? (warning, joining global rooms consumes way more bandwidth)

[alexalok]

1. AFAIK, there is still a flaw that allows to join all clan rooms, so I believe this it is not a good idea
2. If there are 2+ joined rooms, require 3rd argument which is either room_id or all
3. Personally, I would use this command only for joining global rooms, but in general autojoin would not only consume more bandwith but also spam debug output, so I think all "joins" should be explicitely required by user.