Support "webvr polyfill" style virtual reality on mobile browsers with a native WebVR

[blairmacintyre]

Want to get the cardboard-style VR supported on mobile for doing stereo VR.

At this point, it is unclear if we want to support stereo AR on mobile devices with only one camera: in Argon4, we opted for "stereo" where the same video image is shown on both eyes. That may be sufficient for simple demos, but has issues when an object is up close.