Create attachments when performing an import

We need to attach the "assets" provided from the data dump to the aaib
reports as attachments, and replace their references in the body text.
Replace original markdown with govspeak for attachments
Force summary to a temporary string for the moment
WIP - Update to account for new schema, move test data across to fixtures so the build passes
Move import implementation to app/importers (+specs)
Repo is not required in the attachment import mapper