Interface Elements
We will use the Graphical Interface Builder to add five interface elements
needed by the scrolling list: two dragareas: "list" and "scroll_bar" (one for
the list and one for the scrollbar), two buttons "list_up" and "list_down"
(one to scroll up in the list, and one to scroll down), and one field:
"list_fld". The width and height of "list_fld" determing the width and height
of a list item.
