Private games

[jsnell]

It'd be great to have an option for private games, rather than games that are open for anyone to join. Right now the only way to do that would be to add something to the description field to discourage random players from joining. But there will always be somebody who doesn't read the description...

Typical ways I've seen this implemented on other sites are:

• Games with a fully or partially pre-populated player list.
• Password-protected games (only players who know the secret handshake can join the game).

[tobymao]

I'll work on this after I finish implementing rolling stock v2. If someone joins that shouldn't be there, you can boot them.