Django 2: Switch from MIDDLEWARE_CLASSES to MIDDLEWARE
Django 2: Switch from MIDDLEWARE_CLASSES to MIDDLEWARE

This also slightly changes the order of the middlewares according to Django's
current default value and the django-debug-toolbar docs:

https://django-debug-toolbar.readthedocs.io/en/latest/installation.html

("You should include the Debug Toolbar middleware as early as possible in the
list.")

See:
https://docs.djangoproject.com/en/3.0/topics/http/middleware/
https://docs.djangoproject.com/en/3.0/releases/1.10/#new-style-middleware

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