New handtracking video passtrough feature proposal.

[XenoPL]

Once passtrough is implemented, ALVR could use handtracking video passtrough feature similar to one in VirtualDesktop. It's two small round areas of video passtrough following users hands. See VD demo video: https://www.youtube.com/watch?v=F5gdMI2cBwk

It's handy when user is trying to reach for keyboard/mouse or other items while still being in VR.