Add teams

Should be possible to add opponents via config so that players are automatically assigned to them when they join, and also to fix the "Invite All Opponents" button in team matches.

And also finally implement Bancho teams? (probably a separate issue)

Ideally teams would be exposed to the front-end to create matches via drop-downs instead of having to type team names. Also Challonge integration would matche to configured opponents by names.