Fix 6% of unknown files; Classify 7,249 .NSDstat files

[raprasad]

• similar to 12,400+ of "unknown files" are ".xz" - Mark them appropriately #3333

---

7,249 of files with known extension .NSDstat are marked as unknown.

Fixes:

• Now: Mark these as related to the Norwegian Center for Data Research.
  • http://www.nesstar.com/support/faq.html
• Later: If we can read these files and/or get the DDI, then re-crawl, and save the metadata appropriately

  - Depends on prototype json schema endpoints for file metadata (sloan project) #3088

 {
        "extension": ".NSDstat",
        "count": 7429,
        "total_count": 124357,
        "percent_string": "5.974%"
  },

[mheppler]

Related to #2202

Also make sure these files have the proper MIME type to display in the cards and facets.

[pdurbin]

Closing in favor of #2202