Fix adminmedia templatetags (Review Board).

The old "admin_media_prefix" tag is deprecated in favor of just using the
staticfiles framework with an "admin" prefix. This change fixes up Review Board
to handle that.

Testing done: Viewed all of the changed pages.
Reviewed at https://reviews.reviewboard.org/r/4629/
Move the "You have comments in other revisions" blob into javascript.

This change drives the rendering of the info box for comments in other revisions
from javascript instead of HTML. This is the last piece of the diffviewer
needed before I can do dynamic updates.

Testing done:
* Created draft comments on several diff and interdiff revisions and verified
  that it appeared correctly.
* Tested in conjunction with my change for dynamic updates.
* Ran unit tests.

Reviewed at https://reviews.reviewboard.org/r/4626/
Simplify the webapi test function names.

This removes all the redundancy in the test function names, in order to
shorten them. The type of resource has been removed from the names. So,
instead of test_get_file_attachment_with_foo, it's just
test_get_with_foo.