Sort Pull Request Overview By Recent Activity

Sorting the pull request overview "feed" by recent activity will improve usability.

If someone responds to my comment, I have to scroll all the way down to the comment's original position in activity feed. I can't even `CTRL+F` to find it since the feed lazy loads. So, I end up mashing `END` until I hit the bottom of the feed. Then I `CTRL+F` to find a comment. But if replying to a comment or editing one made its whole thread appear at the top of the feed, I could spend more time actually reviewing prs instead of managing them.

If I add a comment on someone else's pr, I have to send them a link to the comment when they've forgotten about it. If the feed were sorted by recent activity, though, I could just reply to my own comment (e.g. "Reminder to look at this."), which would make that whole thread appear at the top of overview feed.

I made some screenshots. Here is a comment thread where the most recent comment (well the only comment) is from three days ago.

Note the position in the vertical scroll bar.

Here is a comment thread where the most recent comment was two days ago, same pr:

The thread with older activity appears above one with newer activity, which makes my life much harder.