Reversing camera for truck [SP]

With this mod you can look back throw the left window when you are reversing with truck and trailer (like in ETS2).

v1.1added controls for position of reverse camera
- you can now use reverse camera for any vehicle instead of truck only
- helptext will show when reverse camera is active, you can enable/disable it by NUM_0
- setted position of camera will be saved for current vehicle in your savegame

Controls: KEY_KP_0 - show/hide help controls
KEY_KP_minus - move camera outside
KEY_KP_plus - move camera inside
KEY_KP_multiply - move camera forward
KEY_KP_divide - move camera back
KEY_KP_period - reset position of reverse camera