Polytoria's first physics based car.

For now, you can only drive aimlessly, but I'm planning to make this game a racing game.

Controls:
- R to reset the car

Known issues:
- The curved ramp doesn't work well. I can't do much about it. Raycasts with meshes are a little bit bad on Polytoria.
- Character is not well placed in the car. I can't place it lower otherwise it will collide with the colliding box of the car, and so it breaks everything.