Cosmetic improvements, controller support, and a new car setup!

Hello buggy racers! This update is a bit bigger than usual. Most notable are the cosmetic improvements and the new car, but it also features a bunch of smaller fixes and improvements. Also, more steering wheels should be supported now.

• added cosmetics: wall/track transition shading, track wear before corners, trackside houses, adboards
• overhauled input system. should support more joysticks/wheels now.
• overhauled toyato86: less wobble on accel, but also less stable, harder to drive
• moved toyato 86 & audo quattrus to new difficulty class, added new car to it too, the chevra comora
• improved obstacle placement algorithm. should be less in the way
• AI crashes into walls a little less often during battles
• dust particle intensity a bit higher, configurable in graphics options
• built with newer unity version, let me know if you notice any regressions!

I hope this version is to your liking, and if not, let me know! Especially if you have any problems/regressions with your controller/gamepad/steering wheel - since a lot has changed in the input code,

Cheers! Bastiaan