add published at to dsu schema
Rename published_date to first_published_at
Merge pull request #301 from alphagov/feature/add-published-at-to-dsu

Add published at to dsu schema
Remove gemfury
Merge pull request #304 from alphagov/remove-fury

Remove gemfury
Add RAIB Report doctype schema

This commit adds the doctype schema for Rail Accident Investigation
Branch reports as published by Specialist Publisher.