Issue-758: Revise and update Kryo serialization mechanism

- update of the Kryo library to the latest version
- use an external library to get common serializers (for immutable collections)
- simplify the encoding process (no more multiple attempts)

Tested on a basic flow: login for a service, ST validation, logout
You're right: I don't see the use of serializing registered services. It's certainly for the tests.