interface ControlpanelListener
is a collection of messages send by instances
of Controlpanel or their child windows
(Taskpanel its implemented by TaskManager
instances of three different classes are needed
to run TimeSlice, an instance of
TaskManagerwhich manages the data of
the tasks, furthermore an instance of Mainframe
which is the 'Frame' of the GUI of TimeSlice
and last the TaskTimer which calls specific
update routines periodically