World loc and office links on doc pages

For: https://www.pivotaltracker.com/story/show/42850055

When a doc has world locations and worldwide orgs attached to it, we present a series of links instead of just text.  Of course, this should respect a feature flag, so we've also renamed the existing ``Whitehall.world_location_news_feature?`` to just ``Whitehall.world_feature?`` and we can use that to control this sort of thing.

NOTE: when we deploy to production/staging make sure we merge alphagov/alphagov-deployment into release as there is a new initializer to set the new feature flag to false.