Create a directory of blessed demos that perform well

[jdm]

We're going to need to create a homepage for our HoloLens builds that only contains demos that show off FxR to its best potential. Right now those are:

• ball shooter
• lorenz
• painting
• manish's dragging fork (https://manishearth.github.io/webxr-three/webxr_vr_dragging.html)

If we can get the interaction in the color picker working then it might be useful to include as well. The same goes for the drumming demo, except that the stereo rendering is still clearly bonkers.