Add a toggle for average system size

[wakystuf]

To clarify: Size here means "# of planets" not "Average size of the planets" Would likely need to kill the "galaxy age" setting in order to make this work Potentially would provide people flexibility instead of forcing the override with other mods that will cause conflicts Note that we'd always still have >0 systems of 1-2 planets, even in the highest settings, to avoid breaking certain quests (and possibly other mechanics that I'm forgetting)

[captaincobbs]

This sounds good to me, how would you go about it?