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.