Build search and information pages

Adds search and information page for organisations

Story: https://www.pivotaltracker.com/story/show/73388408

This isn't exactly what the list of documents is - some of the documents in the list may not be related directly to the Cabinet Office.  A more accurate description would be:

Then I should see a list of sub-sectors in which some documents are related to the Cabinet Office organisation, with a list of documents in each sub-sector.