Add revoked and expires properties to JsonWebKey context.

[msporny]

This PR attempts to address issue #182 by adds the revoked and expires properties to JsonWebKey context. It also differentiates the anchors for expires on proof and verificationMethod.

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[OR13]

@msporny this seems like a great places to remove confusion over "verification method revocation" and "credential revocation"... we get this question a LOT... and it would nice to be able to share a note to a comment regarding this. something like:

verification method revocation time information can reveal information about a controller. credential status do not include timing information, because it can degrade the privacy characteristics of some status lists... there is not formal relationship between these concepts, etc....

[msporny]

Agreed, I'll add that text to that effect in a future update to this PR.

[msporny]

Added in c4aede2.

[TallTed]

The language we developed later is better, and should be applied throughout, as here.

[TallTed]

According to @iherman in w3c/vc-data-model#1262 (comment)

the domain expired is set to both (i.e., the union) of Proof and VerificationMethod.

Note that expires rdfs:domain Proof, VerificationMethod does not set rdfs:domain to the union of Proof and VerificationMethod, but rather to their intersection; that is, any entity with the property expires must be both a Proof and a VerificationMethod.

For the apparently intended union, where an entity with the property expires could be either a Proof or a VerificationMethod, rdfs:domain must be changed to schema:domainIncludes.

Suggested change

	domain:
	- sec:Proof
	- sec:VerificationMethod
	domainIncludes:
	- sec:Proof
	- sec:VerificationMethod

[msporny]

@iherman would have to add this to the yml2vocab tool, as I don't think it has a domainIncludes property? Thoughts, @iherman?

[msporny]

Normative, multiple reviews, changes requested and made, no objections, merging.