Super hacky webvr support

[Manishearth]

don't merge this, it breaks a bunch of things.

To use:

• Open the 3d demo in Chrome Canary for Android with webvr enabled (chrome://flags)
• Select an AA strategy other than 4xSSAA (this hits memory limits and needs investigation)
• Click the VR button twice . This is due to a bug in how chrome determines if a VR request was initiated by user action
• Put the phone in your Daydream and press the home key on your controller
• Connect a physical keyboard to navigate. Yes, really.

The AA breaks down at a distance and shows fuzzy stuff, so you'll need to move closer to the monument to see text.

Will work on a proper mergeable PR later.

[Manishearth]

https://github.com/pcwalton/pathfinder/pull/76