Feature request: submission form field for URL

[kmccurley]

I can't say that I've thought this through all the way, but we had a request to add a URL field to the submission form, so that resubmissions would provide a link to their previous submission. It's possible that there might be other uses for this like in the review form. I could always override the Text_PaperOption type, but it's not clear how I would do validation (not just as a URL, but as a URL that points to a previous HotCRP submission). I think the Text_PaperOption is also used in search so we may not want to reuse that. One way to address this is to add a regex validation field like what exists for openreview. Another way is to just use <input type="url"> but that is much less powerful.