API: Return "status" and "started" as separate fields

[cuu508]

The web UI displays "up + started" and "down + started" states by showing a an animated progress spinner under the "up" or "down" icon:

In comparison, the API currently cannot express the "up + started" and "down + started" states. The API returns a single "status" field with the possible values: new, started, up, grace, down, and paused. Therefore custom dashboards are disadvantaged compared to the standard web UI (see healthchecks/dashboard#8).

Update API to return two fields:

• status = new|up|grace|down|paused
• started = true|false

This would be backwards-incompatible change so would probably have to go under /api/v2/.