FITS Media Type doesn't have an RDF Mapping

[dannylamb]

Discovered this with a large-ish workbench ingest. It's not the biggest deal in the world, but because there's no RDF mapping, Milliner indexing fails for FITS files and it can clog up the queue with all the retries that are also destined to fail. This leads to derivatives taking way longer to generate, and can give the impression that it's failed to make them instead of just being super slow.

The fix is to add an RDF mapping for the FITS media type, and then to add the FITS media type to the "All Media" context so that it's RDF gets altered accordingly.