Split and clarify the builtin workflow into a pure front-end part and repository/common part.

The builtin addon has become a workflow that is both front-end and has a repository internal part. The front-end should become a workflow like any other, possibly having a regular pojo repository workflow. The REAL internal workflow should only have stub components in the common and repository and the actual
implementation should be inside the repository. This is possibly clarified by moving
addon/builtin/repository
addon/builtin/common
into the repository/ tree and have a new addon/builtin/repository that only chains into the builtin workflow.