Link to the Org from a specialist document

With certain documents, users will generally be linked straight to that document and want to know that it comes from that Org. This commit adds a `DocumentPresenter#organisations` method which pulls them from the
content API response, a helper to render them as a links in a sentence and updates the view to display them.

[Ticket](https://trello.com/c/B8KLPUa6/387-drug-and-device-alerts-and-dsu-documents-should-be-tagged-to-the-mhra)

Screenshot:
![screen shot 2014-10-31 at 14 36 25](https://cloud.githubusercontent.com/assets/449004/4862286/5519a8d2-610b-11e4-961c-f646bd8e3ab1.png)