…efault which is supported by Django 4.2

This is needed since Django 3.2

Update Django-TinyMCE to 3.6.1 which updates TinyMCE from 5.10.1 to 5.10.7

…ango-tinymce package.

The link was wrong in case Pytition was not installed at the root
of the webserver, which is what happens on YunoHost.

for instance if it's in http://domain.com/pytition/ instead of directly in http://domain.com/

One must use `reverse()` which takes care of adding the `script_prefix`
and not just put a hand-crafted relative uri as argument to `build_absolute_uri()`

This was because the logic was to show the first pane containing errors.
And the fields of the style pane were not declared as optional in the StyleForm.
Therefore the fields were marked as "errors" "this field is required".

Mark those fields as non-required.

See: fabiocaccamo/django-colorfield#145

…of the model, not the form.

The tab was shown as selected only when clicked, but since this is
the default tab it should be shown as selected by default.

This is a known unresolved issue in Bootstrap 4
See: twbs/bootstrap#23454