Redis-limpyd-jobs

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* Manage consequences of race condition in get_queue

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* Correct a bug when add_job try to manage duplicate jobs

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* Manage failures when a worker is requeuing delayed jobs
* Add job's PK in worker logs
* Delete the "queued" flag of a job if failure during add_job

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* Add a `queued` field to the `Job` model to enhance avoiding multiple same jobs to be added

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* Add missing scripts module in package

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* Correct bug passing queue_model/error_model/callback to worker script
* Tweak logging