Published events cannot be deleted
Steps to reproduce
Steps to reproduce:
1. Go to Recordings->Events
2. Try to delete an event that has been published
A modal window ask the user to select a workflow for event retraction, but does not offer any workflow so that the event cannot be deleted
A workflow that retracts the events should be offered
Workaround (if any):
There must be a workflow with the tag delete-ng that (at least optionally) retracts the publication.
This feature (prevent user from deleting published events since there would be no way to delete the distribution artefacts) was introduced by PR 627.
delete-ng should also be added to workglow documentation