Add MinRange plumbing to attack activities.
Added MoveWithinRange activity for Mobile units.
Use MoveWithinRange for attack activities.

Fixes #2104. Fixes #2923. Fixes #4455.
Only inset range for mobile targets.
Simplify MoveAdjacentTo pathfinding.
Merge pull request #5617 from pchote/attack-moveadjacent

Improve unit-attack movement