Expose a client's session ID

[m-oben]

Context

At server side, connecting clients are identified via their sessionId, provided by the server. This works fine.
At client side, there is no such ID available. It would be useful to identify clients in a similar way.

Solution

A client actually already owns such an ID in its Session. Therefore, we should simply expose it.
Moreover, similar to how the server behaves, said ID could be passed to any Profile's handleRequest method instead of null currently.