Add Google Analytics to 404, expired job, and debug pages [RD-47]

Also adds tests ensuring that tracking only appears on pages that it should appear on.

Grabbing the path for the jvguid is done in JS. We don't create 404 responses manually (they're created via get_object_or_404), so we can't pass that information in from the view. The simple template tag I created seemed to not work as well.

All tests pass.