feature: allow chairs to undo negative ratings after review is fixed

[dants]

Sometimes, reviewers who receive negative rating(s) fix their review and resolve the problem. It seems, however, that negative ratings typically persist despite such fixes, presumably because those who assigned them rarely go back and check if something has changed.

In such cases, arguably, it would be productive to allow chairs (often the ones who asked the relevant reviewer to fix the problem) to undo the negative ratings.

If there's a way to do this, I've missed it.

Thanks, --Dan