R1:7ae33d14ec7b

Use new Differential bucketing logic on default (non-dashboard) homepage

Summary:
Ref T10939. If you haven't installed a dashboard, we show an "Active Revisions" panel on the homepage by default. I waited a bit to update this, but the new buckets don't seem to have caused any major problems so far.

Update this to use the new logic. I'm just showing "must review" + "should review", which is similar to the old beahvior.

Also replace the notification count with this same number. This is a little different…