Support for different cull modes

Normally, culling is enabled for non-doublesided objects. By default, back-face culling is enabled so that only the front facing polygons are drawn. I ran into a case where I needed front-face culling (needed the inside of the sphere to always face the camera even when the camera was outside of the sphere - essentially an inverted sphere).

I added a simple boolean field called `mBackSided` which determines whether the backside shows (frontface becomes culled) and calls `glCullFace` which determines cull mode.

I'm not sure whether the normals should be inverted in this case. Let me know if it does.