Added drawing of "caps" to the start/end of each line drawn; cleaned up and reorganized code; light optimization pass

The PolyfillControls helper has some breakage where it doesn't
always use the polyfilled VRFrameData class. Also, we don't even
want the pose data to be applied to an Object3D, so it seems a
little bit silly to use.

This was renamed in three.js r93.

If it is, don't allow user to enter in 2D. Instead, prompt the user to copy the URL and open it in Safari.