Initial support for Occulus head-tracking via WebVR

Although there is no formal specification of the api yet, some Firefox and Chrome devs have published experimental builds implementing a close minimal api:
Firefox: http://blog.bitops.com/blog/2014/06/26/first-steps-for-vr-on-the-web/
Chrome: http://blog.tojicode.com/2014/07/bringing-vr-to-chrome.html
Added support for VR rendering via WebVR

The distortion is now handled by the navigator.
We only retrieve the field of view and ideal render target resolution for the current hmd and setup a double camera node.
The dualcam has been updated, you can press f on a supported navigator with an oculus and it just works.
Merge pull request #84 from Teybeo/feature/WebVR

WebVR