Proposal: Simplify and reduce @context for v2 to reduce issues -- change the context so we only define terms that are mentioned int he core spec

[ptsefton]

I think our approach to the @context could be improved in v2

By mixing Schema.org and other terms we opened the door for some confusion. Eg we imported the Portland Common Data model hasMember/memberOf props into the RO-Crate context, but these were subsequently added to Schema.org with a different (much less generic) meaning.

I propose that we:

1. Only define terms that are used in the spec name, description, etc
2. Define schema.org as the default vocab, but stop importing all its terms into our context, thus reducing the current significant overhead on writing RO-Crate libraries
3. Add some prefixes, pcdm, bioschemas, rdf, rdfs to the context but mandate that these should be used with the prefix like pcdm:memberOf -- stop trying to import these things into the core RO-Crate context and let the other projects look after them
4. Make it clear in the v2 spec that name, description ETC MUST resolve to the correct schema.org URI.