Updated the notification system. Main changes are:

- the notification system is now a service, p3Notify, that is a public RsNotify.
- RsNotify does nothing except providing a registration system for new notify clients.
- Clients should derive a notify client from the NotifyClient class and register it to rsNotify
- all registered clients get all notifications, so only derive the needed methods. This should allow 
  plugins to get notifications as well.
- updated the code to call RsServer::notify()->[notification method] from inside libretroshare
- pqiNotify has been removed.