Draco compresion support

[akella]

Hi! First of all thank you for this plugin, even tho i dont have textures on my preview, its a huge life saver for me.
Just wanted to let you know that:
If models are compressed with Draco, previews are not generated.
I suppose because SceneKit did not include Draco decoder at the moment, but i saw one here https://github.com/3D4Medical/glTFSceneKit.
Unfortunately i have zero experience developing in Xcode, but may be you, or some of the users can make a PR with it.
Thank you for this plugin again! All the best.