Rework of vehicle repair/install/remove times.
Added some comments.
Adds a missing part.removed check to fix a crash (tiles only)
Merge branch 'fix-crash-part_id_string' of https://github.com/vidarsk/Cataclysm-DDA into merge
Merge branch 'feat-veh-modify-times' of https://github.com/vidarsk/Cataclysm-DDA into merge