Structured heartbeats

[savagematt]

It would be nice to see how far through a job an agent is in the UI, e.g.:

{:current_ticker "VOD"
 :tickers_processed 234
 :total_tickers 2345
 :seconds_per_ticker 0.02}

We can allow agents to report back on progress of the job in their heartbeat message.

The server should hold onto only the last heartbeat message so we don't fill up the database.

Exposure of more detailed logs is covered elsewhere. Toshy should not become another mediocre log processor.

[savagematt]

In fact, the heartbeat metrics could include a URL where the complete logs of the agent can be found. A URL to Kibana or similar.