Even more car AI in unity

Code is now simplified, got rid of gears, neighbours are only searched for once at the beginning, corners are handled better now as well.

Also, if the car ever faces away from its destination it will find a new way round rather than reversing into the front of another car.

A couple of crashes with lots of cars but to be honest that's not too bad considering they all ignore each other. Next step is obstacle avoidance.