Panorama example needs to be updated to use CSS3DArgonHUD.js

[blairmacintyre]

The panorama example is not putting HTML buttons on the display in the "preferred" way, but using the Argon HUD renderer. Thus, it doesn't support the stereo viewer correctly, and relies on the current implementation of the way argon.js interacts with the DOM.

We should have our samples written in a way that encourages people to follow our preferred way of doing things, even if this approach works for this particular example.