* src/glade-property-class.[ch]:
  o Added new member weight.
  o glade_property_class_get_displayable_value() returns is now const.

* src/glade-editor-property.c: adapted to the new
  glade_property_class_get_displayable_value() declaration.

* src/glade-editor.c: Fixed bug 345893. "Need to order
  properties in the editor and widget-groups in the palette"

* src/glade-widget-class.c:
  added glade_widget_class_properties_set_weight().

* src/glade-xml-utils.[ch]: added glade_xml_get_property_double().

* src/glade.h: added new tag GLADE_TAG_WEIGHT.

* widgets/gtk+.xml.in: set weight in several properties.
  GtkWidget's tooltip, GtkBox packing properties, GtkButton GtkImage