Django-user-tasks

* Check DB connection atomicity before closing "dead" connections.

Have the `start_user_task` receiver close obsolete connections before starting the task.

* Fix issue where `ordering` attribute of the `UserTaskArtifactAdmin` and `UserTaskStatusAdmin ` classes must be a tuple or a list but was a string.

* Make the model list views in the admin panel more useful.
* Routing Python dependency upgrades.

Make ``UserTaskArtifact.url`` a ``TextField`` with a ``URLValidator`` instead of a ``URLField``.

* Upgrade requirements.
* Change ``max_length`` of ``UserTaskArtifact.url`` from 200 to 512.