Refactor code

[user-grinch]

Notes:

• [ ] Try to reduce compilation time
• [ ] Improve the way JSON is handled
  • Load data as structs
  • Do something about typeid(std::string)
• [x] Make calculations independent of frames per second ( delta time )
• [x] Reduce unnecessary class inheritances, combine them into one? (Paint.h, vehicle_render.h, pool_object_renderer.h)
• [ ] Improve data sharing between classes
• [x] Improve the situation with hotkeys ( Add options to enable/ disable a particular hotkey )