Fewer lines almost always better.  Also, we don't want to spread
these out unless we have to.

Known issues:

  - Error rate tooltip computes over whole range (sum), should be per second or per minute or so
  - Duration buckets not great. Should also be per second probably.

They're only example but they scare me when they show up in grep results

We have enough numbers with little value already

Make everything more consistent and generally more nice.
I am a bit proud of this now.
Let's hope it holds up.

Rationale: These are servers, they should be transmitting mostly.
But really it's rather arbitrary.

- Add node exporter to nodes
- Make the old nixpkgs 19.09 node exporter work (amend config)
- Fix a typo (??) and exclude monitoringvpn in network traffic graphs to prevent double counting

... and make path an option.

  sed -i 's|var/secrets|run/keys|'

See Ops#193