Update for the changes to djblets static media.

This pulls in the stuff required from the djblets static media move. Part of
this means that we'll re-ship the djblets media as part of the Review Board
package, but that's fine.

Testing done:
* Verified that pages like the dashboard and extension list still worked and
  looked correct.
* Ran build-media.py and checked the results.

Reviewed at https://reviews.reviewboard.org/r/4655/
Fix comments in the diff viewer.

When I refactored everything to let the diff viewer change revisions without
reloads, I broke comments on the diff page pretty hard. This change fixes it
and cleans things up a bit.

Testing done:
Verified that I could see comment flags (and the associated comment
tooltips/dialogs) on the diff page for various revisions and interdiffs.

Reviewed at https://reviews.reviewboard.org/r/4677/