Add lobby password option alternative.

[nani]

Add an alternative option to make games private by allowing to access your game (and hence your IP) to only buddies you have as host.

Why would this be a desirable alternative:

• It would get rid of the need to know the password
• It would allow all your buddies to join automatically
• If designed right it would allow for new cool hypothetical cases as
  • tournaments: only allowed players for each match would be allowed to go in + arbiter or streamer
  • lobby admins allowed to join a rated game or similar to resolve problems
  • Temporary allow some users in your match if not buddied
  • others?
• As is done now if you want to have a big game (ex: 4vs4) and not have a public due DDOS (or DOS) attacks everyone must know the password and having to pass it to each player can be very difficult as most only use lobby or forum as chat medium

How would be implemented:
The current password system seems to be sending the password to the server doing the client verification there, then returning a deny or allow. With this it would either need to know the buddy list of each player (which is inefficient and unrealistic) o an alternative, which would be to send a join request from the server to the game host with all the corresponding information needed and let the host return a allow or deny response, which will be forwarded to the client by the sever.