Added Session class which can be used as a Dictionary key to find the previous version of the same Session, replaces AnnouncedOrigin
Renamed AnnouncedSession to SessionAnnouncement
Added SessionChangedEventArgs, all CollectionChanged EventArgs from AnnouncedSessionCollection derive from this class
SapClient: detect interfaces when they are added/removed while the SapClient is already enabled
Connection, Origin: bugfix, field mix-ups