Added through keyword for nested structured relations.
Added through keyword for nested structured relations.

normanjaeckel/OpenSlides,normanjaeckel/OpenSlides,OpenSlides/OpenSlides,ostcar/OpenSlides,ostcar/OpenSlides,tsiegleauq/OpenSlides,tsiegleauq/OpenSlides,ostcar/OpenSlides,OpenSlides/OpenSlides,normanjaeckel/OpenSlides,tsiegleauq/OpenSlides,normanjaeckel/OpenSlides