Add unpredictable number to JS ZK proofs

[jot2re]

The JS part of issue #167.
See section 2.2.1 in the Token-negotiator report.
See Jira issue 291.

[micwallace]

@jot2re I'm keen to catch up about implemting this and packaging the JS library for use in TN and attestation.id. Message me on discord when you get a chance next week.

[jot2re]

@micwallace sorry I forgot to write you. This issue is still relevant. Currently the flow allows reuse of ZKPs. However, it seems like a very minimal change to get this fixed. I can try to make the changes needed in Token-negotiator and authenticator, but given I don't really have TS expertise I will need some help throughly validating and testing such changes. Let me know when you have time to look at it.