Change Ofqual slug to match search term

Ofqual was initially created as the unabbreviated version but the title is Ofqual, and that's what people think of it as and search for.

This commit adds a data migration which updates the slug, along with all of Ofquals Users and Editions which they've published.

This will also require a bunch of changes in Production environments which I don't have access to.

[Ticket](https://www.pivotaltracker.com/story/show/80284724).

When deploying:
- [ ] update the Org tag in Panopticon
- [ ] update the Org slug in Signon
- [ ] update the Org in the Need API
- [ ] clear the cache in Maslow
- [ ] update the Org in Contacts
- [ ] update the Org in Transition and Redirector
- [ ] tell Search and Browse about the change
- [ ] add the organisation redirect to router-data