[Meta] Ping list location filtering issues/improvements

[justinkambic]

There are several issues we have noticed with the way location filtering works on the Ping List component today:

1. There can be cases where locations that aren't present on the current monitor show up as options for filtering. (you can see this in the screenshot below; the monitor has one location but many options to filter by)
2. It's not possible to filter by unnamed locations. (also visible in the screenshot below)
3. All unnamed locations are grouped as a single monitor (this was a design choice quite some time ago that may be worth revisiting now). It might be nicer to display unnamed monitors as separate entities on the page.