Add an addon setting to not spawn crater/dirt mounds when the aircraft hits the ground

[Lupus590]

We have respawning aircraft on our training map which can be online for days at a time. If our players are practicing their AA then they can create a lot of clutter on the map with the crashes. We have the wreaks being cleaned up with garbage collection already but we can't figure out a way to clear up craters/dirt mounds and so we would like a way to prevent their creation in the first place.