Remove left-over CIP tables

we migrated CIP model to be an Edition instead
of being a stand-alone model a while ago:

https://github.com/alphagov/whitehall/pull/1422

this cleans up the tables left behind.
Correct `dependent: :destroy` for CIPs

www.agileplannerapp.com/boards/173808/cards/8853

there's a `dependent: destroy` on organisations to destroy associated
corporate information pages when the organisation is deleted. in spite
of that few orphaned CIPs exist: 336462, 336498, 363483.

there are changes in 2 places to fix this issue:

1. `dependent: :destroy` on `corporate_information_pages` association
   only destroys the record in the join table and not the corporate
   information page edition. so the fix is to have an explicit
   `before_destroy` to clean corporate information editions
   and documents.

2. callbacks are invoked in the order in which they're declared.
   if the `before_destroy` to destroy corporate information gets
   registered before the `:edition_organisation, dependent: :destroy`
   this will work. else, when the callback tries to destroy related
   corporate information pages it won't be able to fetch the related
   corporate information editions because the linking record is gone.
Adding migration to change making-schools-and-colleges-more-accountable slug

The migration changes the slug of the policy document, removes the old documents from search, adds the new paths to search and sets a redirect on the main policy slug.
Merge pull request #1898 from alphagov/remove-cip-tables-from-schema

Remove left-over CIP tables
Feedback to show no editions were found

www.agileplannerapp.com/boards/173808/cards/8827

editors are getting confused and think that editions
filter is not working. also, updated the search results
title to include the classification scope that would be
applied.
Update policy data migration to use prefix route

Use a prefix redirect for the policy change. This will then match all
the supporting pages and redirect them.

Also remove the 'for' from the search index calls. As far as I can tell
the search index gets set based on the object anyway. It was also
causing the migration to fail for me locally.
Merge pull request #1896 from alphagov/feedback-on-topical-event-featurings

Feedback when no editions are found
Re-index statistics announcements on org changes

When an organisation changes its slug we also need to re-index the
statistics announcements as they store the organisation slugs in the
search index. They are like editions in many ways but aren't actually a
type of edition so weren't picked up the first time around.
Merge pull request #1905 from alphagov/org-slug-stats

Re-index statistics announcements on org changes
Merge pull request #1897 from alphagov/remove-orphaned-corporate-information-pages

Correct `dependent: :destroy` for CIPs
Merge pull request #1904 from alphagov/change_schools_colleges_slug

Change schools colleges policy slug