refactor(payload): Simplify JobPayload

* JobPayload is now just a Name and Unit
* Break the SystemdUnitFile data object into its own package
* Move code out of unit package to systemd package that interacts with systemd
feat(job): Implement new Job flow

* Jobs are now submitted, started, stopped, then destroyed
* Lots of refactoring internally to simplify Registry calls
* Drop unused events EventJobStatePublished, EventJobStateExpired
* Rename EventJobCancelled to EventJobStopped
Merge pull request #66 from bcwaldon/corectl-verbage

Implement new Job flow