Add support for RAIB reports

This PR contains the work in specialist-publisher for editors from the
"Rail Accident Investigation Branch" to publish reports. It contains:

 - the schema of the possible values of the facets in the RAIB Report
   form
 - the models, services, observers, repo and views for RAIB reports
 - adding RAIB editors to permission checker
 - testing RAIB Report workflow
I actually disagree with tommy here -- I think this should be singular because that's the name of the finder (see https://trello.com/c/Mtd6YDSr/371-raib-finder-add-support-to-rummager-and-finder-api-for-raib-reports-1)