This example program shows how to use

 - different types of buttons
 - different types of groupboxes

The buttons which are used are radiobuttons, checkboxes (also tristate
checkboxes), normal pusbuttons and toggleable pushbuttons. These
buttons are seperated in four groups using groupboxes. The example
shows how to make a buttongroup totally exclusive (only one button can
be checked), exclusive for radiobuttons only or non-exclusive. It
also demonstrates how buttons (and other widgets) can be laid out
in rows and columns using a groupbox.

