Added schedule for publishing to actor
Editions scheduled for publishing can't be edited

... and making the method used for validation private
as it is not being used outside. conveys intent clearly.
Editions scheduled for publishing, can't destroy
Dynamically define scopes based on states

needed to define one for scheduled_for_publishing,
ended up doing this.
Adding status_text to accomodate more details
Add cancel scheduled publishing workflow action
Transtion to published state from scheduled