Show publication sub-type on HTML pubs

https://www.pivotaltracker.com/story/show/46978235
updating to use display_type which works for consultations too
moving the doc type from the h1 to its own p
Merge pull request #535 from alphagov/add-doc-type-to-html-pubs

Tracker: https://www.pivotaltracker.com/story/show/46978235

Show publication sub-type on HTML pubs