Make /lobby work for all game modes

[STK-FabianF]

Description

The command /lobby, known from soccer tournaments, should work in all game modes. This is helpful for Hide and Seek servers.
Obviously, it should only be available for hammer people, maybe even only as part of /power2?

[STK-FabianF]

Might also be interesting to be able to force only particular players to lobby. Not sure it's possible. But would be helpful in regards to server moderation, e.g. if someone is gamethrowing, instead of kicking, just force this player to lobby ...