Add exclamation mark/visual element to tags with new updates

[timlod]

We will be indexing many pages in cd. If there happen to be many updates (which may not be the case), it could be useful to go select a bank first (via tag), based on a small visual indicator that there are updates inside that tag.

This issue is probably lowest-priority because once the differ is complete there shouldn't be that many updates day-to-day.