ToolButton: add 'icon_name' as a GObject property SL #3658

Sugar ToolButton inherits from Gtk.ToolButton but is not overwriting
'icon_name' property.  So 'icon_name' can be passed to the constructor
of Sugar ToolButton but the result is different than setting it via
ToolButton.props.icon_name.

Signed-off-by: Manuel Quiñones <manuq@laptop.org>
Acked-by: Simon Schampijer <simon@laptop.org>

src/sugar3/graphics/toolbutton.py

@@ -120,6 +120,8 @@ class ToolButton(Gtk.ToolButton):
         self.set_icon_widget(icon)
         icon.show()
 
+    icon_name = GObject.property(type=str, setter=set_icon)
+
     def create_palette(self):
         return None