Show whether a talk is new or has already been edited

[yoe]

When sreview works in anonymous reviewing mode, the overview page contains links to videos that are to be reviewed, and reviewers are expected to click on those links and do review.

It may make sense for them to know whether a review is a first review or whether it is a confirmation of something that has already been reviewed. To do so, a simple ✔ (if so) or ✗ (if not) in the review table showing whether corrections exist already would be nice.

[yoe]

Now that the database contains a "changes" counter, this should be reasonably easy to implement.