Unstack troops in ground combat

Right now though troops are immobile and can't mount engines, so we would need to give them a default speed (say, 1). This could be a setting in Settings.txt with a default of 1.

This would make ground combats much more watchable, and also make range matter when it comes to troop weapons.

But what if all the defending troops are unarmed and they run away? Then the planet will never be conquered...