First attempt to implement cart simulation

Added the car prefab from
http://blogs.unity3d.com/2014/01/17/new-sample-assets-beta/
Fixed some wheel collider issues.

Wheel colliders moved to center of car when starting, making it tip to
the side.
Merge branch 'master' of https://github.com/Double-Fine-Game-Club/bad-golf-community-edition
Tuning the cart
Merge branch 'master' of https://github.com/Double-Fine-Game-Club/bad-golf-community-edition
Moved cart on level_01 so it doesn't fall off
Merge branch 'master' of https://github.com/Double-Fine-Game-Club/bad-golf-community-edition
Made cart prefab and not rely on MainCamera
Merge pull request #64 from Slimliner/master

Fixed so the cart is a prefab that can be added easily