Add definitions for w3id.org/security

[OR13]

w3c-ccg/security-vocab#41

To be super clear... absence of vocabulary definitions in the default constants causes signature suite verification to fail without a custom context extension:

  {
      '@context': 'https://w3id.org/security/v2',
      type: '/JsonWebSignature2020',
      created: '2020-06-18T16:11:39.964Z',
      jws: 'eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..4HSj-IJY6pyrA-pvEZPHnaXmSb-ITLxi-GdslQATe1ovDOhDpPxDRg_-xlUdBBWUyX0wCH-L1Ij5pJmoESISDQ',
      proofPurpose: 'assertionMethod',
      verificationMethod: 'did:key:z6MkpP568Jfkc1n51vdEut2EebtvhFXkod7S6LMZTVPGsZiZ#DTXI1UCGeLHx3B6GmZtMQuR8b3KDdaayEYPJN8iME6o'
    } JsonWebSignature2020

note the type: '/JsonWebSignature2020', !== JsonWebSignature2020

This can only be fixed by adding the context defintions to the document you are signing:

this causes compactProof: false, to be required.

[OR13]

@msporny note the use of documentLoader here https://github.com/w3c-ccg/lds-jws2020/blob/master/packages/json-web-signature-2020/src/__tests__/vc-js-tester.ts#L23

This is related to digitalbazaar/vc#80

When passing a custom document loader, I expect to be able to mutate https://w3id.org/security/v2 and see what it would look like if the security context included the new terms... however, https://w3id.org/security/v2 never gets hit.

I believe this is caused by:

https://github.com/digitalbazaar/jsonld-signatures/blob/ee999c814fcbac15ea9ae86e56f9b127c544c970/lib/ProofSet.js#L74
https://github.com/digitalbazaar/jsonld-signatures/blob/master/lib/documentLoader.js#L19

[OR13]

I'd prefer to not see this kind of short circuiting of the documentLoader and instead, ship a default document loader, and make the library consumer intentionally choose to use it (make documentLoader a required argument, with no default).

[OR13]

AFAIK, this has been addressed