Improve refresh behavior of the PR views

[RMacfarlane]

Currently data within the extension can sometimes get out of sync, two specific examples:

1. In the extension, you start a review and add some comments inline in editors and submit the review. The PR author responds to them on GitHub.com. If you open the description page from the extension after this, the reply appears on it. The editor comment thread does not update immediately, however - it takes up to 5 minutes for this to poll and refresh even though we should already know there is another comment.
2. If you have the "focused mode" setting on and you use the "Merge" button there, the view updates, but if you have the description view open, it does not