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- Drop support of Django<2.2. Now it supports only Django>=2.2,<4
- Drop support of Python3.5. Now it supports only Python 3.6, 3.7, 3.8, 3.9
- Drop support of ``DJANGO_MODERATION_MODERATORS`` setting
- Formatted code with `black`
- Drop dependency `django-model-utils` which we used for Choices functionality
- Add partial support for Django 4.0 - remove ugettext, change `smart_text` to `smart_str`,
change `ifequal` template tag to `if`.