Reversing camera for truck

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

If you find any errors or issues, let me know in comments or to kenny456@seznam.cz and i will fix it in next version.