This method is called only if you
implemented IwodXMPPNotify interface in your application,
and wodXMPP.Notification
property has received reference to
instance of your implementation.
Called each time when your contact changes his online
status. When this happens, the notification method will
provide you with two parameters, Contact - which
provides you with the reference to XMPPContact object of
the contact that changed his status, and OldStatus
which provides you with information what your contact's
previous status was.
If this contact is only from some chat room, ChatRoom
argument will hold reference to the chat room.
When your contact is connected more than once using different
resources, Resource
property will contain all of them, but first one listed there is one
that caused this method to be called.