Attachments for other document types

With the introduction of other types of documents, attachment services need to be generalised. This involved removing the call to specialist_document_id and allowing the document_id to instead be passed in.

This PR adds an AAIB Reports Attachments services registry, controller and uses the same views, with the only change being paths for partials and a switch for the breadcrumbs in the attachment pages.

This also refactors out some steps to be a bit more generic and adds a cucumber test for the AAIB Reports Attachments workflow.
Would this helper be better located in the attachment helpers?