Provide PublicationType.statistical helper and use it

So we don't have to remember that Statistics and NationalStatistics are the stats types, and so there's only one place to change if we add a new one.
Allow for world_locations as filters in routes

Nothing has been done to make the DocumentFilter action these params though.  There are big changes incoming, so it feels like it's not worthwhile (yet).
Show more editiony things on world locations show page

Pull in publications (broken down to stats and non-stats), policies, announcements, and show a recently updated feed box.  Makes it have content more like the organisation page although there's not much actually shared between the two views.

Pulled in styling as best I could too to make the page look more like the organisation page too.  This definitely needs tidying up.
Use render collection: for rendering shared/featured_news

Make use of the defined counter to provide item-n extra_class stuff too.
Make edition world locations have stronger featuring capabilities

E.g. more like edition organisations.  I think we're calling out for some shared behaviour here.  Problem is we don't want to change urls for existing images.
Copy featured state of world location associations onto new editions
Remove document featuring UI from world_locations#edit page
Provide featuring UI for world locations as standalone page

So it's more like the doucments tab for organisations and the featured items page for topical events.  Borrows heavily from their views / implementations too.
Update world location frontend show page to use new featured items
Features to describe world location featuring workflow
Add styling to world location pages

- Extracted recently updated styles from topics, topical events and
  organisations into a helper. Used that helper to style the block on
  world locations.
- Extracted the documents grid out of organisation pages so it could be
  shared on world location pages.
- Added descriptions to priorites and improved the markup so its clearer
  as to what markup will get produced.
Remove article group and section as no longer used
Fix featured_news partial so we don't keep adding to extra_class
Share styles for featured news

Share the styles for featured news blocks. This is now styled the same
on topical events, organisations and world locations. Shared the base
styles between the three of them and 'enhanced' it with each's own
requirements.
I don't need a hero

I'm not holding out for at hero 'till the end of the night.

Not used anywhere anymore. No more heros.
Update cucumber test for new featured image size
Don't use featured_news_articles in world_location_test.rb
Merge pull request #177 from alphagov/recent-docs-on-world-locations

Recent docs on world locations