Removing a duplicated JSON file
Adding slug to placeholder manuals
Adding Manual Index view

Also removing call in controller to render show
Using web_url from Manuals

Also adding to placeholder Manuals and extracting sections out to behave
like Topics and Organisations
Making breadcrumbs work for other manuals

This refactors the way the breadcrumbs work to allow them to work with
other manuals. This also refactors the document presenter and extracts
the section group and section presenter to other files.
Merge pull request #38 from alphagov/breadcrumbs-for-other-manuals

Add breadcrumbs for other manuals