Support multiple versions of relying party api

[felix-hellman]

Our current implementation is not interoperable between api versions. If session data for an older version is loaded an exception will be thrown and vice verse when an older version of the application tries to load a newer version.

This issue suggests the implementation of backwards compatibility such as a newer version of the application can handle older sessions. Updating the service a new version should be able to handle an old session and route it towards the old api version.
If an older version tries to read a newer version of the data model of the session an exception needs to be thrown.

Relates to #259