Store hand position relative to body orientation/position.
Get the base position/orientation directly from the avatar to prevent
jerkiness when flying with the Hydra.  Also, restore arm lengths when the
Hydra becomes inactive.
Merge branch 'master' of https://github.com/highfidelity/hifi
Merge pull request #1595 from ey6es/master

Fix hand jerkiness when flying (by always keeping the hand positions relative to the body orientation/position).