rif-id-core RequestedCredentials should save hash returned by server

[jessgusclark]

The hash created by the server to hold the Requested Credential request should be saved into the reducer and database. For now, the hash can be retrieved with this:

const getHashByRequestId = (id: string) =>
  dbConnection.then(connection =>
    findOneCredentialRequest(connection, id)
      .then(response => (keccak256(response.message.raw) as any).toString('hex'))
      .catch(err => console.log('hash error', err)),
  );