Django-task

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* TaskAdmin: postpone autorun to response_add() to have M2M task parameters (if any) ready
* Task.clone() supports M2M parameters

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* property to change verbosity dinamically

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* util revoke_pending_tasks() added

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* DJANGOTASK_JOB_TRACE_ENABLED setting added to enable low level tracing in Job.run()
* Added missing import in utils.py

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* cleanup: remove get_child() method being Task an abstract class
* fix: skip Task model (being abstract) in dump_all_tasks and delete_all_tasks management commands
* generic get_model_from_id() helper
* Job.on_complete() callback

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* provide list of pending and completed task status