MECH, VehicleClass++, IWYU script & cleanup

- include-clean script using include-what-you-use to detect unused includes
- errors detected by Eclipse analyser fixed
- ozCore
  * HashSet: removed freeChain() and value copying in copyChain(), still present
    since forking from HashMap
- matrix
  * VehicleClass settings subclasses for various vehicle types
  * MECH vehicle type, STATIC -> TURRET
- FIXME
  * fix pilotPos rotation in MECH