Show topical events in the doc header for editions that have them

Rather than having them be passed in (like topics and policies) it just detects them from the document (like role appointments and world locations).  It's not clear why we do one over the other.
Regenerate locale files for new heading
Merge pull request #561 from alphagov/show-topical-events-on-frontend-docs

Show topical events on frontend docs

https://www.pivotaltracker.com/story/show/48826873
Merge commit 'a896601ee2ed69c77d6e563de4bc9a09c5d74ea7' into HEAD