Support attachments on world location news

Also changed the default way of rendering govspeak to use
govspeak_edition_to_html. This does the same thing as
govspeak_to_html, but parses attachment tags if the document
supports it.

https://www.pivotaltracker.com/story/show/58083090
Merge pull request #951 from alphagov/58083090-support-attachments-on-world-location-news

Support attachments on world location news