feat(deisctl): add deis cluster control utility

The `deisctl` utility wraps `fleetctl` to help simplify Deis cluster operations. Over time, there are a number of other things we would like this to do.  For now it implements:

* `deisctl install` - install all Deis units
* `deisctl uninstall` - uninstall all Deis units
* `deisctl start/stop <component>` - start or stop components by type or identifier (e.g. router or router.1)
* `deisctl scale <component>=<num>` - scale component to specified number (e.g. router=2)
* `deisctl status <component>` - print systemd status for Deis unit(s)

The `Makefile` targets and `README.md` should be fairly self-evident.

Please note that this PR is not yet intended to replace to `Makefile` targets currently wrapping `fleetctl`.  I'd like to have this merged and tested alongside our current workflow so we can get an understanding of what else it needs to do before it can replace what we have.