Add possibility to let player choose their tribes in scenarios

[GunChleoc]

The Smugglers scenario now can be played with any tribe, but the players need to manually hack the map packages for that.

Add an option to the game setup screen so that players can choose their tribes. Map editors need control over whether tribes can be chosen by players in their scenarios.

[Benedikt Straub (nordfriese)]

Setting the tribe for a scenario player to "Random" can currently cause a crash. How about interpreting "Random" tribe for scenarios as "choosable" in the game-setup screen?

[GunChleoc (gunchleoc)]

Yes, that's possible. Empty tribe is interpreted as "random" by non-scenario games and by the editor, so we could leverage that. This would have the advantage that there will be no change in the data packets.