Provide enhanced options on deletion of parent objects

[Guite]

Description of the new feature

Follow-up to #11 - instead of hiding the delete functionality or aborting the deletion process if an object has related children, it is possible to let the user choose from some extended options to proceed with, like

• abort
• continue with deleting everything (first the children, then the parent)
• continue with reassigning the children (example: delete a project and reassign existing tasks to another project)

Feature Benefits

More convenience during more complex structure changes.