Failing feature: unpublishing with a title change

I don't like this feature, but I couldn't think of a better way to
accurately replicate re-titling, publishing and then unpublishing a
document in the way that is causing the bug.
Add new fields to Unpublishing
Wire up views and controllers
Remove rogue save_and_open
Fix hash syntax
move super user to factory definitions
Simplify unpublishing scenario
Correct slugs and edition types for existing unpublishings

The few existing unpublishings had lost the information about the
original url, because the title of the last edition has been changed.
Merge pull request #255 from alphagov/unpublishing-with-title-changes

Unpublishing with title changes

https://www.pivotaltracker.com/story/show/44711329