Improve heartbeat so it doesn't lie

[jadudm]

The heartbeat process is running in a Gofunc. As result, it is possible for a service to report it is healthy (in the heartbeat thread) when really, the main thread is unhealthy.

We need Work in each service to periodically update a variable or value, and use that as a flag for the heartbeat process, so we know when the last time we productively did work was.

This will tell us, for example, if we ever encounter a situation where all workers have died, etc.