Some basic physics

I've integrated some basic parts of the bullet engine. However it is far from functioning properly. I thought I'd commit it anyway, so that I do not fall too far behind in revisions, since I started working on rev 8, and so that you can see how far I've come at tomorrows meeting.

All necessary files from Bullet are included (and probably a bunch of unnecessary ones too, I'll try to sort them out sometime later), so you should just be able to build it.

Some strange things to note about this version:

-The wheels aren't positioned properly

-Steering does not work properly

-Controls are kinda crappy

-It's still a box driving on a plane, no advanced meshes