Allow the user to pick a workflow stage

[mauromsl]

At the end of the back content workflow, the user has the option to publish the newly submitted article.
If we added a choice element to select a wofklow stage, editors would also be able to quick submit an article straight into production or any other stage.

• Add a selector for article stage
• Re-create all wofklow elements for the given article until that given stage
• Ensure fields such as publication date are not required when the article is not set to "published"