Bullet, use Model instead of Mesh

I just pulled the 3D changes and notices that the bullet tests don't work anymore. It's because the ObjLoader now returns multiple submeshes. So I updated the tests to use models instead of meshes and changed bullet to allow direct construction from a model (it's very easy to work with now).

I haven't looked into the SoftMeshTest yet.

It also contains some minor changes to the 3D stuff for easy constructing a still submodel (by default it has no material, which gives a npe).

And the test use performancecounters now.