Geometry sandcastle examples

I added a sandcastle example for each geometry type.  In order to keep these from cluttering the other demos, I put the existing demos on a 'Showcase' tab, and put the new geometry examples on their own tab.  I moved the 'All' tab to the end of the tab list.
I also enabled horizontal scrolling with the mouse wheel to all tabs, previously it only worked on the first tab.

This is to accompany the geometry and appearances tutorial I'm working on.