Hand tracking support

[JonnyOThan]

Apparently this already kind of works, but we need to support grip and pinch gestures.

Need to test with Virtual Desktop and ALVR

Arbel reports that the fingertip collider seems to be in the middle of the finger instead of the tip.

Pinch actions should be triggered whenever the thumb and index fingertips are close together.

[Arbel-arad]

virtual desktop:

• supports hand tracking, but only "grab" and "pinch"
• all fingers behave correctly but it is sometimes difficult to flip toggles.
• dials can be used by setting "pinch thumb" to the trigger.

ALVR:

• full multi-finger support with grab, pinch and can fully differentiate between all fingers.
• finger positions are accurate with hand tracking, but are not reset if you switch back to controllers.
• dials work with the same settings as VD but the collider is in the thumb tip.

[JonnyOThan]

Virtual desktop has lots of issues with hand tracking and I won't try to support it for now. ALVR is amazing though.

I just added support for activating the pinch action if your current control mode supports partial skeleton tracking. Future work is going to have to come later.