Make the schedule workflow orthogonal to branching workflow

The CMS uses only the hints 'publish' and 'depublish' in org.hippoecm.frontend.plugins.reviewedactions.PublicationWorkflowPlugin to find out whether '(de)publish' and 'schedule (de)publish' is enabled. When publish is enabled, also scheduled publish is enabled.

However, when there are branches, we want to disallow scheduling workflow (unless we choose to allow scheduling for a branch). The only way to add this is add to the scxml a seperate hippo:action for scheduledPublish and scheduledDepublish