add a mechanism for clearing setup readings

[williamcodes]

As an installer,
When I go to the setup page for a hub,
Then I see setup readings for only the sensors I have connected that day,
And I do not the setup readings from weeks before when it was tested.

Notes:
We talked about doing this by adding another column to the database on the relay server, maybe called "hidden". Then we could flip the bit in that column to clear it. This could be done with a script. A simpler option would be to only show cells that were last seen less than 24 hours ago.

[williamcodes]

The more I think about it, the more it seems like we should just do a quick fix in the view that hides everything more than 24 hours old.