Allow single build, multiple pushes

[Darhazer]

If we want to deploy the same image to multiple apps, currently it requires each one to run the whole build/push/release phase.
Even on a single app, one has to push the image to both the release and web workers, making it two build/push/release builds, wasting CPU time that way.

It would be great to be able to split those and build only once, and then push multiple times the already built image.

UPDATE: Just found out that 1.4.0 supports multiple process types. It at least allows for single build for web,release. The option for multiple apps however is still missing