Add generic Parlamentsspiegel-Export Importer

[robbi5]

After Sachsen, who provide us a customized parlamentsspiegel export, now Berlin made one available too: https://www.parlament-berlin.de/de/Dokumente/Open-Data

There should be a generic importer for Parlamentsspiegel-Export files.

Little bit of Documentation (german): https://www.parlament-berlin.de/C1257B55002AD428/vwContentbyKey/W2B8QFZ9774WEBSDE/$FILE/Doku%20Pardok%20XML-Export.pdf