Implement Limbo, or Observer, mode

[andy5995]

Yes, many games nowadays provide a Spectator mode.

I think for that, what we should have is a "Limbo" menu. You open this to change teams or join spectators, example: https://et.clan-etc.de/wolfguide/images/limbo_menu.jpg

When we support objectives etc this info can be shown on the larger map view, too.

I think it would be good to go implement this, however new UIs should not be using hard-coded offsets and things, we should have a Table component for example that can do layouts.

Originally posted by @winrid in #90 (comment)