More code optimizations
- Added a new function unit_stop_stepaction which completely cleans up a planned action
- The new function will now be called when a new action request is received and when changing the map
- Removed setting of "chaserange" as part of the step action system as it's no longer used
- Changed check_distance functions to return "bool" rather than "int"
- Special thanks to Cydh for pointing out possible optimizations