Add Rotation Offset option for Thumbs for Leap Motion

[ZornTaov]

I have a model whose hand is rigged like so, and when I enable the Leap Motion tracking the model's thumb is rotated maybe 45° into the hand, this means I'm unable to, say, do a thumbs up motion. Finger tracking for curling and splaying the fingers works fine, but the thumb is offset for whatever reason. Adding maybe a slider (or three for xyz) for thumb offset should maybe fix this.