Provide option to hide existing items

This follows up on #10
> The third case is when there are things to do, but they are one or more pages beyond the current offset.

In such cases, an option to hide lines with existing paper items would make it clear(er) whether there are any missing paper items for a given author. Example: https://orcid-scraper.toolforge.org/results?qid=Q56433929&orcid=0000-0003-2338-4564 — there is nothing to curate on the first page, but there may well be things to do on later pages.