Warn, then delete file attachments when changing group settings

[fcheslack]

To avoid orphan attachment items that would no longer be possible to create with the new group settings, before a setting change that disables files is applied the user should be asked for confirmation, then all attachment items should be batch deleted on the page before the setting change finally goes through.

https://forums.zotero.org/discussion/75310/option-to-purge-group-library-data

[dstillman]

As noted in https://github.com/zotero/dataserver/issues/30#issue-154864497, the best way to find these currently is to do a search for ?itemType=attachment and then look for .data.linkMode being imported_url or imported_file.

[ntnsndr]

Thanks for doing this. Stuff from group libraries is really clogging up my hard drive. I just turned off syncing of Group files. Two questions:

• When will this update appear in a release?
• When it does, will I have to do anything further, or will it automatically remove the orphaned files?

Thanks for all your good work.