Avatar interaction

You can now reach out and bump someone's face -- their avatar will lean to avoid the touch.

The hand-face collision test has two main problems:

(1) Collision currently uses the collision proxy of the "hand" joints, which are actually located closer to the avatar's wrists.

(2) The head's collision proxy is hard-coded to be a 15cm radius sphere, so if your avatar has a  funny shaped head then it won't collide correctly.