I am starting to clean up the mess that is Global right now, and to implement a clean...

I am starting to clean up the mess that is Global right now, and to implement a clean infrastructure
for storing settings (session-wide and local). First step: Instead of putting synchronization stuff into
Global and doing special treatment for signals in Core, we have now a clear interface for handling
session-wide data in both Client and CoreSession:

Client::storeSessionData(key, data) [static]
Client::retrieveSessionData(key, defdata) [static]
CoreSession::storeSessionData(key, data)
CoreSession::retrieveSessionData(key, defdata)

CoreSession also cares for persistent storage using QSettings. It should be noted that the client-side store function
just sends a signal to the core, and the client-side data is actually updated upon receipt of the sync signal from core.
IOW, stuff is not stored immediately, and you should thus not rely on it being available right after your call to
storeSessionData(). If this is a bad idea, we might change this behavior at some point.

Note: The code has not yet been tested thoroughly, and it's only the first step anyway.