Solid shapes

[Vavassor]

#3

Adds solid boxes, spheres, meshes, capsules, and rectangles.

[Vavassor]

Still to do:

1. Add documentation comments to the new drawing methods.
2. Add polygon or depth offset to the solid shaders to prevent z-fighting when mesh colliders overlap the visible mesh of the object.
3. Move ellipsoid generation to its own static class.
4. Some index and vertex generation code could be shared between capsules and UV spheres.

[Vavassor]

The above 4 tasks are finished.

I realized mesh generation was unnecessary for most shapes. Left the generation files in, but unused. They could be useful in the future for a retained mode API.

Now working on:
5. Update the sample scene to display solid shapes.

[Vavassor]