Put palettes into the "default" palettegroup by default again. (fix #4084)

src/sugar/graphics/palette.py

@@ -248,6 +248,8 @@ class Palette(gtk.Window):
         self._leave_invoker_hid = None
         self._right_click_invoker_hid = None
         
+        self.set_group_id("default")
+
         # we set these for backward compatibility
         if label is not None:
             self.props.primary_text = label