Feature request: add a search field `lastupdated` for when a paper was last commented on

[msridhar]

This would be useful so a user could do searches with show:lastupdated and sort:lastupdated, just like what is possible now with timestamp. This could be helpful, e.g., to chairs to find papers where a discussion needs to be revived, but I think it could be helpful to reviewers as well. You can achieve this now via the API, and then paste the paper IDs back into the search box to get the ordering you want. But, it's a bit slow (need to fetch the comments for each paper in a separate API call, as far as I can see) and adds an extra external step.