feat(cmd): use tabwritter to line things up

So pretty

```
UNIT			LOAD	ACTIVE	SUB	DESC	MACHINE
web@8000.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
web@8001.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
web@8002.service	loaded	active	-	-	a7a91602-369c-453b-8953-dceb75bdf3e6
```
refactor(target): Rename target pkg to unit
refactor(unit): Break out Target from unit.go into manager.go
refactor(unit): Rename Target to SystemdManager
Merge pull request #20 from philips/pretty-tabs

feat(cmd): use tabwritter to line things up
refactor(unit): Move all local systemd/filesystem access to SystemdManager
refactor(unit): Break out dbus path serialization and test it
refactor(unit): Solidify contract between Agent and SystemdManager

The Agent should always be passing around Job objects, not
job names.
refactor(unit): SystemdUnits are responsible for fetching their own Payload
feature(cmd): Add corectl status command
Merge pull request #22 from bcwaldon/manager-refactor

Refactoring of local Systemd management
refactor(corectl): Expose loaded state based on presence of JobState
Merge pull request #23 from bcwaldon/corectl-start

feature(cmd): Add corectl status command
feat(state): Expose LoadState and SubState in addition to ActiveState
Merge pull request #24 from bcwaldon/moar-state

feat(state): Expose LoadState and SubState in addition to ActiveState
chore(fmt): Run go fmt across the codebase
feat(registry): Add Registry.GetJobPayload method
feat(corectl): Add cat command
Merge pull request #25 from bcwaldon/corectl-cat

Add 'corectl cat' command
refactor(scheduler): Rename scheduler pkg to engine