prototypes: apply force on proper position.

The position was taken like if the vehicle hadn't moved/rotated at all.
prototypes: applyForce() in world coordinates.
prototypes: store mass and moment of inertia inverted.

Setting them to 0 makes the object non-movable/non-rotable without any
need to change the equations.
prototypes: removed superfluous forces.

Applying weight force to center-of-mass, not splitting engine forces to
tangent and normal. Friction is currently omitted, will be implemented
later.
prototypes: implemented applyImpulse().
prototypes: initial collision detection.

Need to compute proper TOI, as the vehicle currently creeps out after
some time.
prototypes: removed artifical rotation controls.
prototypes: visualization and parameter tweaks.
prototypes: move the vehicle up a bit to show some interaction.