Ensure all our rdfs: properties are defined in core RO-Crate profile

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As pointed out in #466 we use rdfs: properties however these are not all defined in the core RO-Crate profile. This adds rdfs:comment, rdfs:label, rdfs:subClassOf, rdfs:subPropertyOf with links to the RDFS specification, which inconveniently is not resolved from the @id itself. I've also added definition of domainIncludes and rangeInclude and used these here in schema.org-style-schema way.

As this is not modifying the spec itself, I think it's sufficient to version as a patch update (1.2.1).