Revert detailed guides heading on topics

https://www.pivotaltracker.com/story/show/53343067
Split publications block on topic page

"Publications" block has been split into  "Publications",
"Consultations" and "Statistics" - same as orgs.
Refactor document list partials

There no material difference between the way announcements and
publications are listed on pages. This consolidates the two partials,
which allows topics#show and topical_events#show to be DRY'd up
Pull out helper for incrementing
Use new partial on topical_events#show
Merge pull request #905 from alphagov/document-list-partial-tweaks

topics#show partial tidy up
Manually merge branch 'iterate-lists-of-documents-on-topics'

Conflicts:
	app/controllers/topics_controller.rb

Tracker: https://www.pivotaltracker.com/story/show/53343067