Fix docs generation properly.

My previous fix for docs generation didn't actually work. It just
appeared to, due to my test conditions.

We now set RUNNING_TEST = True in settings, which is where it should
go. The Makefile no longer has to set it.

make clean also now removes the database, and this is called when
fixtures change.
Move DiffFileIndexView out into its own file.

This isn't used anywhere except the DiffViewerPageView, but neither are any of
the other views that make up the diff viewer, and the page view implementation
is a pretty big file.

Testing done: Smoke tested the diff viewer.
Reviewed at http://reviews.reviewboard.org/r/4642/
Add some very simple tests for the parse() methods in diffviewer models.

The diff viewer has several new models that aggregate bits of data required to
build the page. This change adds unit tests for the parse() methods, which
convert the names in the webapi into javascript-style camelCase names.

Testing done: Ran js-tests.
Reviewed at http://reviews.reviewboard.org/r/4643/
Add API for working with drafts of diffs.

There was no way, through the API, to get an existing diff uploaded as a
draft. One could be created by issuing a POST, and the payload would be
returned, but the links to the resource in that payload would result in
a 404 due to the diffs resource not showing draft diffs.

This fixes this by introducing a new
/api/review-requests/<id>/draft/diffs/... tree that mirrors the public
/api/review-requests/<id>/diffs/... tree. Diffs that are part of a draft
will link there. The client can inspect this to see everything that will
be published.
Pull 1.7 release notes images into the docs tree.

The images used for the 1.7 release notes were all hosted on reviewboard.org.
This was both annoying in terms of things being self-contained (we'd have to go
upload things separately from writing the docs), and the format of them was
pretty bad when building the docs to a format other than HTML.

I've downloaded all of the images and referenced them locally instead of
remotely. In addition, I've added some conditionals to include the full images
when the target isn't HTML and fixed the latex target.

Testing done:
* Built the HTML docs and verified that the thumbnails showed up, and that
  links to the full versions went to the correct place.
* Built the latex docs, compiled to PDF, and verified that the full screenshots
  were included rather than the thumbnails.

Reviewed at https://reviews.reviewboard.org/r/4646/