Reduce API calls from bulk dismissals

Problem/Motivation

Bulk dismissals ("Mark all like this as OK") generate a separate JSON API call for each dismissed item. That's a lot of DB activity.

If there are more than ~25 issues dismissed at once the editor may leave the page before the back-and-forth finishes, and calls may time out.

Steps to reproduce

Find a page with links to 75 PDFs. Dismiss all...

Proposed resolution

Rewrite the API to allow for a concatenated write.

Remaining tasks

...learn how to rewrite the API to allow for a concatenated write, or pass the request to a batching queue. Each dismissal is stored in a separate row.