A group-box panel arranges its subwindows in a single column, but also
draws an optional label at the top of the panel and a border around
the panel content.
Unlike most panel classes, a group-box panel’s horizontal and vertical
margins default to 2.
Creates a group pane whose title is label.
If style includes 'deleted, then the group panel is created as hidden,
and it does not affect its parent’s geometry; the group panel can be made active later by calling
parent’s add-child method.
The font argument determines the font for the control. For information about the enabled argument, see window<%>. For information about the horiz-margin and vert-margin
arguments, see subarea<%>. For information about the
min-width, min-height, stretchable-width, and
stretchable-height arguments, see area<%>.