Allow parent group owners to edit lesson documentations/etc. of courses

Add a rule (linked to a preference) that allows parent groups owners (e.g. 09e) to edit lesson documentations for courses (e.g. 09e D).

added part::backend source::customer type::feature labels

assigned to @yuha

created branch 215-allow-parent-group-owners-to-edit-lesson-documentations-etc-of-courses to address this issue

mentioned in merge request !276 (merged)

assigned to @nik and unassigned @yuha

assigned to @yuha and unassigned @nik

closed with merge request !276 (merged)

mentioned in commit 14c6c8f0