Allow new format types for specialist documents

When formatting SpecialistDocuments for panopticon we now export them with specific formats so we access this information within the contentapi.

This branch relies on the following pull request or specialist-publisher will throw a validation error from panopticon.
https://github.com/alphagov/panopticon/pull/184

This will also require republishing of all AAIB reports and CMA cases in order for panopticon to register existing urls with the correct format.