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.

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.