Ability to view CSS VR content properly in 2D mode

[caseyyee]

It's very difficult to make a CSS VR layout work in both 2D and VR. The reason for this is that we share the same properties to manipulate elements in 2D as we do in VR.

A solution to this would be to create a completely separate coordinate space to work with elements in VR. This could be done using element attributes or new CSS properties (rather than conflating the existing translate3d)