Frustum culling

Added the ability to do frustum culling
Yes, and probably we could use this minimal approximation to extract the frustum planes:
http://www.iquilezles.org/www/articles/frustum/frustum.htm

But if you don't mind I let this for future PR's. I'm getting solid visualization with the current implementation. Also I have to send a PR to read from a .osgjs file as well as a PR for the osg plugin.