Re-enable & improve

• PublicationWorkflowFunctionalTests#publishSingleRootPage. etc.
• WorkflowUITest#changeContentsAndRejectWorkflow

Those have been disabled recently due to often failures.

The later maybe can be replaced or just ditched.

In any case check whether tests in  old test-class WorkflowUITest are already replaced within new test-class PublicationWorkflowFunctionalTests