Django-fiber

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- Nothing changed yet.

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- Checked compatibility with Django 4.0, 4.1.

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- X-frame-options change broke the page editor - see 289.

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- Django 3.2 support.

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- Add missing .py extension to newly added migration. Really fixes 278

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- Django 3.1 support
- New migration (required because the Page model is based on django-mptt, and django-mptt has removed a number of
indexes from fields - django-fiber itself has not changed). See 278