Make Systraybar a proper subclass of Area.
Make Clock a proper subclass of Area.
Make Global_task a proper subclass of Area.
Make Task a proper subclass of Area.
Make Taskbarname a proper subclass of Area.
Make Tasbar a proper subset of Area.
Make Global_taskbar a proper subclass of Area.

Also, make the Area::clone() hack a bit less horrible by removing unnecessary
casts.