* Database migration: Fix attachments with unexpected structure
* Attachment cleanup: Remove all attachments with no data field
* Export: Allow user to cancel out on error if never succeeded
* Only update attachment id if fileName not present
Turns out that modern attachments only have fileName, without an id.
* A small tweak to the attachment fix-up migration, test coverage
* Take migration version back down to 16
* Jshint fix in database.js