map entitiy properties to schema.org things

we should have a mapping of marketplace entities (and their properties) to schema.org. we can then include jsonld metadata on the item detail pages.

i have started with MPDataset, help apprectiated:

Dataset	dataset
label	headline
description	abstract
description	description
accessibleAt	url
???	includedInDataCatalog
properties: keyword	about
licenses: label	license
version	version
contributor: actor.name	contributor
dateCreated	dateCreated
dateLastUpdated	dateModified
properties: language	inLanguage