Only generate slugs for english html attachments.

To prevent slugs being generated with non-ascii characters etc.
Add cuke for viewing recently published documents
Rename all_announcements_link to see_all_link
Add see all links for all latest document blocks

Includes organisations, world locations, topics and topical events.
Add controller and route for latest documents
Add LatestDocumentsFilter

Exactly matches the way the recently updated documents are generated for
the latest blocks on home pages.
Add #to_s methods to orgs and world locations
Fill out LatestController with LatestDocumentFilter
Add pagination controls to latest page
Use heading in the style of history pages
Decorate the collection of latest documents
Remove unused local from partial
Highlight nav sections for latest documents page
Redirect bare requests to /latest to the feed

Ideally a request to /government/latest without any filter parameters
would render a paginated list of all content published in whitehall
in reverse chronological order.

In the near future we will have a single index of published content in
Rummager which will make it a lot simpler to do.
Make #subject and #documents private
Removing 'parent' department from NMD description

non-ministerial departments are currently described as being "of" their parent department. This isn't the case as they report independently to ministers. This removes the implied parent/child relationship.
Fix html_attachments controller to support ids

friendly_id's find overrides weren't working through the `attachments`
association because friendly_id is only defined on the `HtmlAttachment`
class, not the base class.  Adding the `html_attachments` association
enables this to work correctly.
Merge pull request #1304 from alphagov/fix_utf8_attachment_slugs

Don't generate slugs for non-english html attachments
Merge pull request #1299 from alphagov/see-all-latest

See all latest documents

https://www.pivotaltracker.com/story/show/65620588
Remove redundant supporting page cleaning code to fix the build.

The old supporting pages have long been migrated to the editions table
so this code is now redundant.