Allow VENs to initiate re-registration

[juantxorena]

The specs say that the VENs should be able to initiate a re-registration. For that, the VEN has to send a oadrCreatePartyRegistration message with the known registrationID. The current implementation doesn't allow this, the oadrCreatePartyRegistration.xml should add the registrationID and the client code should be fixed.

If needed, I can do a pull request with this and some other fixes related to registration.

[stan-janssen]

Yes, please create a pull request if you can. Thanks.