Allow admins to bypass the quarantine check on media downloads

[turt2live]

Note: this was written using the copy/paste development technique, so may not adhere to great Python standards.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct (run the linters)

[anoadragon453]

Overall LGTM. Only main concerns are regarding documentation and debug-ability.

[anoadragon453]

Could you add some documentation for this somewhere?

Either in the Admin FAQ or a new page about media administration.

[turt2live]

There is? It's on the media administration page in this PR.