Parameterise protocol/host in redirect check

We should verify that the URL is appropriate for the current
environment, e.g. development, test or production.
Failing feature for consolidating edition

New behaviour where consolidated editions are automatically redirected
to the alternative url
Add new unpublishing reasons and mark legacy ones

We have to keep the existing reasons around for the unpublishings
already in the database. This is the simplest way to roll out this
feature. If we need to migrate these old reasons to the new ones, we
can do that as a separate step
Add validations for consolidated unpublishing

We always want an alternative URL when the edition is unpublished
because it is being consolidated. We also always want to redirect if
that is the reason.
Update unpublishing form with new reasons
Failing feature for archiving documents
WIP: Add "archived" state to Edition

Still to do:
  Make sure archived editions are findable in admin filtering
  Update public document view to include archived text
  Prepend "Archived" to public page title tag
Update EditionUnpublisher to archive editions

Depending on the unpublishing reason, the edition is either archived
or reverted to draft.
WIP - get feature passing