1. This is experimental slicing for tf3.
2. Small fix in TGLHistPainter.
3. Small mods in TLGTH3Slice
4. small addition in gltf3 tutorial (commented by defualt) - nice "torus" shape instead of Klein.


git-svn-id: http://root.cern.ch/svn/root/trunk@18963 27541ba8-7e3a-0410-8455-c3a389f83636