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.
This should work:

```
defaultServices := []string{"publisher", ...}
for i := 1; i <= 3; i++ {
    append(defaultServices, fmt.Sprintf("store-gateway@$s", i))
}
```