Make a basic web interface, a'la Blinken

[mikepea]

I quite like the idea of enabling a simple 'green light' dashboard similar to the one I've witnessed in https://github.com/alphagov/blinken

Add a '-l {addr}:{port}' option to set up an http server, presenting each query as a 'light' on the radiator. Red for >1 critical, Yellow for >1 warning (but no crit), Green for zero of each.

We don't have 'OK' data available (as yet), so we can't say '5/123 checks critical' or similar. No biggy.

[mikepea]

73053c5 added a basic dashboard. It still needs some work, so i'm leaving it open to track that.