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
The "Java 7 try closeable" syntax is a pure pleasure ;-) which could be used everywhere we need to close streams (I saw your JIRA on this).