use latest dists for aframe-physics-system and aframe-physics-extras (fixes #269). Fix issue where phyiscal hand attached to cursor-controller wasn't being set properly and also add back hoverable component to ducks.

cleanup events; listen for controller events on the playerRig instead of directly on each controller so we don't have to add/remove listeners every time a controller changes.

switch the super-hands on the controllers back to using action_grab/action_release and support that properly in cursor-controller.