Certain Materials don't export to sketchfab.com

[Bug-Reaper]

The PBR and Normal shader materials didn't get exported to sketchfab. Would you be interested in a PR to fix this. I love the tool so I'd be happy to take a look if you're interested.

[stephomi]

Sculptgl is not maintained anymore, but if you make a PR I'll review it and merge if it works.

PBR painting is limited in sculptgl as it uses vertex color instead of texturing. So if you don't have any UVs (voxel remeshing or dynamic topo delete the UVs for example), the texture export won't work.

[Bug-Reaper]

@stephomi I'll definitely take a look at it. It's such a great tool! Probably gonna take me a while to get around to it, but I'd love to start making regular contributions :)