Improve G-Cloud Stagecraft JSON

This commit fixes the page-per-thing key/values used in the breadcrumb,
as well as duplicate the change made in 076be5e32e787105f80f08ee13b1bdf35464b6ec
in the page-per-thing page.
Merge pull request #173 from alphagov/improve-g-cloud-json

Improve G-Cloud Stagecraft JSON