Task Immowelt.de requires a German date format for the expiration date of an energy certificate

Immowelt.de processes the expiration date of an energy certificate differently to the proposals by OpenImmo e.V. They don't process the expiration date in the proposed format MM-YYYY. Therefore the common german date format DD.MM.YYYY should be used for this attribute.

This customization is provided by a new export format called Portal: immowelt.de. Besides this modification the new format provides the same functionality as the OpenImmo-XML format.