Deeper workflow cloning with optional people and tasks

plus a modal for these options when user clicks "Clone Workflow"

* TaskGroupTasks copy when clone_tasks is true; TaskGroups are empty of tasks but not objects otherwise
* WorkflowPeople and Authorizations (WorkflowMember only for non-creator) are created when clone_people is true; only the cloner gets WorkflowOwner otherwise
* TaskGroups get their original contacts when clone_people is true; null otherwise
* Tasks are assigned to their original contacts when clone_people is true; cloner otherwise.