Convert more of the review request views to class-based.
Review Request #9021 - Created June 16, 2017 and submitted
This converts a handful of the smaller review request views to
class-based views, documenting them in the process. This covers the root
view, diff downloads, bug-related views, review request infobox, and
screenshot/file attachment reviews.
Tested each of the views as authenticated and anonymous users. Tested
each code path.
Fixed a breakage in returning HTTP 403 responses on Permission Denied.
Revision 2 (+385 -233)
Checks run (2 succeeded)