feat(publisher): introduce deis/publisher

With this change comes the introduction of the ability to add global
units to the project. Before, we would always prepend "@1" to the units
because we always assumed they'd be scalable. This is not the case for
global units, so I reverted that behaviour.
Yes, but it's ugly. If you wanted to start more than one unit, you'd have to via `store-gateway@1`, `store-gateway@2`, `store-gateway@3`. They'd all start in parallel, though.