Serve uploaded media files with nginx, not django/gunicorn

[yuvipanda]

• Is recommended by django for production instances (https://docs.gunicorn.org/en/latest/deploy.html)
• Probably faster
• Allows for future finetuning as needed
• Does not actually change the static files - only the media files for now. Static files are in the django deployment image and more work.
• The challenge is serving .glb files that are >10Mb, so the nginx improvement is worth it.

Ref #59