Don't update metadata maps with nested nulls.

- Add more tests and assertions
Merge pull request #52 from MastodonC/feature/sensor-metadata

Don't update metadata maps with nested nulls.
Quorum consistency.
Might be able to survive with less consistency.
It helps if you include your session store.
Must be logged in to get at app page.
Mute webutil.
Mute home page logging.
Mute query logging.