test-ui: Allow children expand and fill when packaging in boxes/panes
test-ui: Allow children expand and fill when packaging in boxes/panes

So resizing the main window resizes each widget.

GNOME/grilo,grilofw/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,GNOME/grilo,jasuarez/grilo,grilofw/grilo,jasuarez/grilo,grilofw/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,kyoushuu/grilo,kyoushuu/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo