- Re-organize the return statement of 'NotificationsPage' a bit, otherwise the entire page will reload (blink) every time the drop-down value is changed due to the 'fetching' flag.
- Retained the original behavior of (only showing a blank page + spinner) on the very first load. I think there is merit in not showing the buttons immediately (e.g. when not logged in and `/$/notifications` is accessed directly).
## Issue
Closes 5193: Add filtering on notifications page
## Approach
- Add a combo box, and simply filter out the notifications based on the combo box value.
- Selection state is persistent, but reset to All if there are unread ones when entering the page.
- Tell the user that "no notifications" could be due to the filter.
