add schema.org schema

[pvgenuchten]

This is a feature request to support the schema.org/Dataset schema

Both for import and export

• Export; add a snippet on any html representation of a record, so the search engine can parse it
• Import; Many websites/catalogues advertise datasets in schema.org, would be nice to be able to import that metadata, for example https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/FSSKBW

This needs to be implemented in OSWLib? like iso19139 import, or better to implement here directly?