cherry pick main to dev part 3

changelog/5925.md

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+### Changed
+
+- add ckeditor text size css to make text sizing work
+- add <i> tag to `collapsible-image-editor` Bleach config to allow italic text

changelog/8543.md

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+# Added
+
+- show point field for bplans in the django-admin
+
+### Changed
+
+- adapt bplan api to the requirements for the diplan system
+  - add a new field `is_diplan` to the bplan model to be able to differentiate
+    between old bplans from imperia and new ones from diplan
+  - add the `point` field to the serializer as we no longer need to get it from
+    the bplan map for bplans coming from diplan
+  - calculate the district from the bplan identifier instead of getting it from
+    the bplan map
+  - keep compatibility with the imperia system for now but annotated code which
+    can be removed once the transition to diplan is completed
+  - update the bplan api documentation
+  - add a `bplan_id` field which will replace the `identifier` field once the
+  switch to diplan is done
+  - remove char limit for name and description field, instead truncate text if
+  too long

changelog/_0003.md

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+### Changed
+
+- `imghdr` support was deprecated in python, so now we use `python-magic` and built-in `mime` to check the filetype of images files for bplans created using the API.
+
+### Fixed
+
+- Bug where tile_image was being used instead of image_url.