Ancient Star - ground combat

I'm back to adding features to the Ancient Star, and ground combat is done. Including bombardment and invasion controls UI.

It was a simple feature and I was saving it up when I get burned up with the serialization business. Numbers, for now, are straightforward, each troopship carries one ground combat unit, colony defenders grow by one unit every turn, up to population limit. Combat itself is similar to space combat but with troop attack and defense values being the same.