Switch to the new Celery API

[hackdna]

https://celery.readthedocs.io/en/3.1/whatsnew-3.1.html#django-supported-out-of-the-box

Celery 3.0 introduced a shiny new API, but unfortunately did not have a solution for Django users.

The situation changes with this version as Django is now supported in core and new Django users coming to Celery are now expected to use the new API directly.

Example Django project using Celery
https://github.com/celery/celery/tree/3.1/examples/django