Implement JwK Signature in DidDoc

[arnabghose997]

https://www.w3.org/TR/did-core/#dfn-publickeymultibase

Steps:

1. Add PublicKeyJwk to verificationMethod.
2. Implement JwK Algo to verify JwK signatures.

[arnabghose997]

Verification Material: https://www.w3.org/TR/did-core/#verification-material

Generating JwK: https://www.npmjs.com/package/jwks-rsa