XRTK - Mixed Reality Toolkit Feature Request

Is your feature request related to a problem? Please describe

The hand tracking implementation of XRTK already calculates curl strength for each finger and hand. Those values are not used for visualization yet though.

It would be nice to give the user a visual cue when grabbing stuff and curling fingers.

Relevant classes:

`HandJointVisualizer

Please check the author's explanation on how NeRF works in his speech in CVPR2020 tutorial:
https://www.youtube.com/watch?v=OEUHalxanuc
His part starts at 3:58:28

I like .ply, it's an easy format that supports vertex colors! .ply files are often used for point clouds, so it could be good to consider point cloud rendering when importing .ply files as well.

Might be able to find a nice library for this on here:
https://github.com/nothings/single_file_libs