Severe violence tweaks

[Thrake]

Severe violence seem to only spawn raiders, natives and the occasional fanatics. This is used in almost all multiplayer games as farmers are too easily annexed. I've seen also 1 hunter in like 10 games.

Yet, there are a lot of other minor types that would be fitting for severe violence I think. Mutants, arachnids, slavers, nomads could all get to be more common with severe violence on. Maybe fanatics too. It would help differentiate more planets.