Replace adhoc non expirable signature by standard JWT signature

This pull request replace the current HMAC signature mechanism by a JWT token signing channel, clientId and Authentication endpoint controlled expiration date.

This improve cross-language compatibility and peer scrutiny on the signature mechanism and require a endpoint controllable expiration date. This also remove delegate built-in "secure compare" and provide future proof controllable signing strength.

This could also provides a secure mechanism to embed business data into the Faye message (like current_user_id), to be used by listener or Faye hook (for presence I.E.)

The Faye::Authentication api changed a bit but nothing major, this not BC though.