Kart controller

(This all happened prior to Godot Wild Jam #44 so the details might be a little sketchy.)

Inspired by a Youtube video (https://www.youtube.com/watch?v=Ki-tWT50cEQ) and Twitter post (https://twitter.com/kenneynl/status/1107783904784715788?lang=en) I thought that using a sphere as the physics body would be a short cut way to creating a kart controller.  

Spent some time trying to create this in Godot, but should have looked first as KidsCanCode had already done this exact thing (http://kidscancode.org/godot_recipes/3d/3d_sphere_car/).

After playing with their demo, I wasn't entirely happy but I pushed on for a while. Eventually hitting into this Godot bug/issue (https://github.com/godotengine/godot/issues/50463) where spheres (or other round bodies) do not roll smoothly over static meshes, particularly where there are joins/seems in the mesh (even if the actual mesh is completely flat).

This could have become a deal breaker except that I wasn't even happy with the controller itself. Despite the bug, the KidsCanCode demo is still playable, but it doesn't feel how I want it to feel, and it's certainly not like Mario Kart in that state at all.

After all this I decided to go with a more custom solution base on KinematicBody and using move_and_slide().

No sliding or surface detection yet, but I'm happy with the results. Temporary assets curtesy of model-resources.com!

Next steps will be to get this controller to a state I'm happy with (sliding, turbos, jumps, reversing, steering) then make a start on the track system.