DRY up use of scopes to find latest editions

There are plenty of controllers that want to find the latest few
editions of a specific type (e.g. the 3 latest policies that have been
published in a world location). There's plenty of duplication in those
chained scopes, so we can tidy things up a fair bit by moving them into
a method and setting appropriate defaults.
Allow #latest_presenters to filter by current locale
Use ternary operator instead of if/else
Don't link to english docs from wales-office.cy

When viewing the Wales Office organisation page in Welsh, you really
don't want to be reading links to documents in English. We filter all
publications and announcements, showing the latest ones that have been
translated, rather than just showing the latest ones in Welsh OR English.
Drop pointless method wrapping a scope

Somebody might quote Demeter at me, but I'll risk it.
Merge pull request #761 from alphagov/wales-office-links-to-welsh-docs

Wales office links to welsh docs
https://www.pivotaltracker.com/story/show/54278086
Add function for determining if an organisation is an NDPB.

There are three OrganisationType object that are Non-Departmental Public
Bodies, it is useful to determine if a given organisation is one of
those.
Import additional data from Public Bodies report.

Adds Public Meetings, Public Minutes, OCPA Regulated, Regulatory Function

Add a migration to add fields to an Organisation.  Update the public
bodies rake task to import relevent data.

Update schema to keep it up to date.
Add fields to Organisatons to edit NDPB data.

If an organisation is a Public Body, ask for optional data on Public
Meetings, Public Minutes, OCPA Regulated, Regulatory Function

Options can be blank as not all NDPBs publish this data and we cannot
assume Yes or No for bodies that haven't given an answer.