Job Runner

I'm starting the goroutine that will consume the job queue from Mongo, launch containers, and report results.

- [x] Implement an `io.Writer` that sends any written content to a job attribute and saves it to Mongo. Pass it in to `docker.AttachContainer()` as stdout and stderr.
- [x] DRY up the egregrious amount of copy-and-paste among the logging messages.
- [x] Make the Mongo polling time configurable.
- [x] Remove the container once the job has completed.
- [x] Extract the result from the container based on the job configuration.