/**
* Notifies users according to their preferences.
*
* @abstract NOTE:Notifications are small messages. No subject and no attechments.
* If you need this kind of elements you probably want to send a mail, don't you :-)
* @abstract NOTE: This is for instant notifications. If you need time dependend notifications use the
* asyncservices wrapper!
*
* The classes doing the notifications are called notification_<method> and should only be
* called from this class.
*
*/
