Show the world organisation in world news admin

Although you could add a world organisation to a world news article, the
show page for the world news admin did not include this data. This
caused user confusion. This patch adds this missing information.

https://www.pivotaltracker.com/story/show/54621194
Show message when edition diff is empty

This is related to the work on redesigning the edition show page.
Editors were confused by the blank diff page, so it now shows a
message when the diff is blank. Also tidied up copy.
Cleanup blank consultation outcomes

In today's view of the world, we want consultation outcomes and public
feedback to always have some summary text. But because we have legacy
responses that might not have a summary, we want to losen the
validation a bit so that they remain valid. To this end, we only
validate the summary is present if there are no attachments present.

https://www.pivotaltracker.com/story/show/54897632
Add data migration to clean up blank outcomes

This is legacy data, created as a result of the way nested attributes
used to be used to add/edit consultation responses.
Close unclosed div tag in Policy view

Silences warnings generated in test.
Merge pull request #751 from alphagov/show-world-org-on-world-news-admin

https://www.pivotaltracker.com/story/show/54621194

Show world org on world news admin
Merge pull request #750 from alphagov/empty-edition-diff

Show message when edition diff is empty
Merge pull request #753 from ElliotJH/silence-warning

Close unclosed div tag in Policy view
Merge pull request #747 from alphagov/54897632-treat-consultations-with-blank-outcomes-as-not-concluded

Treat consultations with blank outcomes as not concluded

https://www.pivotaltracker.com/story/show/54897632