Streamline Docker image tagging

[tomkerkhove]

Streamline Docker image tagging so that you can push "full" images and "preview" images.

The build should:

• Build & push images with the tags latest & version when no tag was specified
• Build & push images with the dev tag and the tag that was specified when queueing the build
• Only build & push images if codebase has changed

Overview

• [ ] Change build spec
• [ ] Update build documentation