Implement support for Draco compression

[my2iu]

It looks like Draco should offer some good compression rates that should push file sizes to be below those of compressed raster formats while still allowing for zooming in to high levels of detail. (It might also be possible to build some custom compression that takes advantage of the way that Omber generates its meshes and colors, but that's probably too much work.)

Here is an example of me playing with one file: chibi-dog.wrinklefree: 232 KB gzipped: 107 KB Draco: 30 KB Draco gzipped: 29 KB (though I was able to compress other files by half though)

Draco compression seems a little immature still, so I'm having trouble evaluating whether the contents of the files are correct or not though.

Also look at compression of the indices array, which Draco doesn't seem to do for glTF files yet for some reason.