Added hack to exit scene when Oculus Go goes into standby. Clean up virtual gamepad controls on exit.

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.

add/remove interactable class instead of changing scale and handle rotation correctly with super-spawner; point to duck gltf model in assets repo (and remove scale set in the html)

from 32fc4aba in PR #243