Generate USDZ thumbnails

I recently stubbed out some brutally ugly UI code to render a 3D USDZ file into an animated gif - screen grabbing while orbiting the object. It's far from great or pretty, but should you want to explore and experiment, I made the bits I wrote open source: https://github.com/heckj/Film3D

I wanted the animated gif as a placeholder for documentation content in HTML formatted docs, so I only took it to the point of getting my render and leaving the UI pretty trashy - fair warning.