Web Dashboard Should Show All Sensors that have Ever Been Online, Even if they aren't now

[keenanjohnson]

Currently, the web dashboard only shows sensors that are currently "online", meaning that they have reported data recently.

However, there is a lot of valuable data from sensors that had previously reported data, but had either been moved or went offline.

We should upgrade the dashboard to display all locations that have had measurements reported to give people a better sense of the coverage and dataset available.

[keenanjohnson]

This file contains the DB queries: https://github.com/Ribbit-Network/ribbit-network-dashboard/blob/main/db.py