Bounding Volumes

Hey Dave!

I like to show you my new branch "BoundingVolumesForAll". It is not targeted to the next release, rather I like to discuss the bounding volumes with you. I had the problem, that there are no bounding volumes for some objects (e.g. disk and teapot). So I implemented them. Further I saw the problem for polygon. We need to recalc the bounding volume based on changing vertices. I suggest some solutions in code comments using TODOs. Maybe you think it is worth enough to talk about or to use my branch somehow. Please feel free! :) Feedback would be great!