Django-cast

Wagtail 5 compatibility.

- removed `nb_black` dev dependency
- Support for Wagtail 5
- removed `max-height` from `.cast-image` for bootstrap4-theme because of contortion

Fixing tests for Django 4.0 and make it possible to use custom templates for http error views.

- Fixed a mypy error and added one test for htmx.target is None
- 91 fixed tests for Django 4.0
- Added support badge for Django 4.0 and 4.1 in README
- Updated pre-commit hooks
- 90 added a validation for `episode.podcast_audio` to be set when an episode is published
- 83 make it possible to set custom templates for http error responses

- Extended the tox test-matrix to include Django 4.0
- 90 moved the `podcast_audio` field and added a warning

- 74 Added some documentation for django-admin commands and fixed ``s3_stale``
- Transferred some old documentation
- Fixed language in an image example

Filter fixes + htmx for pagination.

- 88 Fixed date facet is removed from form submit
- Moved app settings init into `appsettings.py`
- Provided some default values for settings which don't have to be in the settings file
- Convenience imports for urlpatterns
- 85 Added htmx support for pagination in plain and bootstrap4 themes

Fixes for theme support and documentation.

Features
- Added support for themes via settings
- Documentation section for settings
- Documentation section for themes
- Installation instructions (not yet complete)

Fixes
- Fixed a bug in the filter/pagination logic 86