Deleting files should not delete from old manuscript versions
Current behaviour: If a new manuscript version is created, and then a file is deleted from that version (either an attachment or an image within the manuscript source), the same file will become unavailable to previous versions of the manuscript.
This is because currently, when creating a new version of a manuscript, files are duplicated by reference only. Deleting a file on one version then deletes the single file that all versions are referring to.
Proposed solution: when creating a new version, all files (both attachments and within manuscript source) should be recreated as new file objects (i.e., a new file stored in S3, and a new file record in the DB)