Allow specification of a default "app notebook" name in the session
Will be created automatically if it doesn't yet exist, and the guid stashed so a lookup doesn't need to happen every time.
Prefs saved in the app prefs directory in a separate plist.
Handle the error if the stashed default notebook guid has vanished; app notebook will be automatically recreated.
Requires exposing the Note.notebookGuid failure parameter out of the exception handler, which should do a fair bit more anyways.