Pinax-images

* fix packaging

* drop dj3.1
* add py3.9 and py3.10
* use path instead of url
* drop deprecation on default app config
* update packaging

* [Release Notes](https://github.com/pinax/pinax-images#401)

* Standardize documentation, badges
* Remove django-appconf from setup.py `install_requires`
* Add third-party libs for isort-ing
* Add trove classifiers

- Revise access permissions for some views:
- ImageSet detail view now accessible by any authenticated user
- Image delete view now accessible only by image owner.
- Image "toggle primary" view now accessible only by image owner.