Push to rift

Hi MrDoob,

I work at Mozilla and we're exploring ways to extend your editor to make it suitable to design VR experiences in the Web. Still not many tools out there except paying ones like Unreal Engine or Unity

This PR is just a starting point to show you things we're working on and start collecting feedback.

I put this together in a couple of hours so it's not ready to be merged but your comments are more than welcome. I added a button that switches the editor to a Rift Mode while pressed. This allows you to tweak your scene and take peeks inside your rift to see how it looks like in VR. I'm going to use vr.js but the rotation of the head is not hooked up yet. You can find a demo here:

http://dmarcos.github.io/three.js/editor

Un abrazo,

Diego.