Add a vaccum process

[wglass]

Should collect and process all of the payloads in the "done" state.

Depends on todo for having the state history of a job be kept in the
job's payload.

some requirements:

• timing data sent to statsd
• job payload is removed from redis entirely
• if [statsd] section not present in config, statsd part is skipped

[wglass]

For now this is best handled by doing stats on-the-fly and making sure the redis operations keep things tight and don't leave stuff behind.