[Schild-NRW] Support "Schnittstelle Schild-NRW" exports

The export function "Schnittstelle Schild-NRW" now exports all data we need, so we can switch the importers to use its data files instead of the custom templates.

added part::backend type::feature labels

assigned to @nik

mentioned in issue #9 (closed)

created branch 51-schild-nrw-support-schnittstelle-schild-nrw-exports to address this issue

mentioned in merge request !110 (closed)

Tried it, then realized the export ha no primary keys or unique identifiers of any kind. Postponing it…

unassigned @nik