feature request: metadata roundtrip

would be interesting to have a plugin for a metadata-roundtrip. Test from any wms/wmts/wcs/wfs capabilities.
For each layer/metadataUrl open the url, check if the metadata has a backlink to the service.

This probably needs individual xpath expressions for schema's such as iso19139, iso19115-1, DC

Expected result:
- Warning for layers that have no metadata-url
- Error for layers that have an invalid metadata-url
- Warning for layers with an attached metadata that has no backlink