live updates for metrics and health check status

[naggie]

• [ ] web app entities
• [ ] web app (failed) health checks
• [ ] service entities
• [ ] service health checks (fail and healthy)
• [ ] healthcheck table
• [ ] healthcheck summary
• [ ] alert triangle (check engine light)

[naggie]

only the progress bar and the value needs updating. "Bad" class needs applying sometimes, also.

[naggie]

over websockets, patches build from object state.

If an unknown metric instance or entity appears, reload the page.