The following files are copied from/based on the icons included in glade3-libgladeui:
 - widget_checkbox.gif
 - widget_checkboxmatrix.gif
 - widget_combobox.gif
 - widget_date.gif
 - widget_file.gif
 - widget_label.gif
 - widget_radiobutton.gif
 - widget_radiomatrix.gif
 - widget_string.gif
 - widget_textarea.gif
