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.
When you say "not tested".. Is this "TODO before deployment" or "TODO when we actually write code that lets us edit attachments for aaib reports" ?