activity.py: Apply sugar GTK3 theme and icon theme

In GTK2, theme name and icon theme name properties could be set in the
GTK2 RC file, at runtime, or by the X settings daemon.

For GTK3, the RC file configuration route for these settings has been
removed. As we do not currently have a settings daemon implementation,
apply these important settings at runtime, early in the Activity
class.

Signed-off-by: Daniel Drake <dsd@laptop.org>

src/sugar3/activity/activity.py

@@ -274,6 +274,8 @@ class Activity(Window, Gtk.Container):
         # This code can be removed when we grow an xsettings daemon (the GTK+
         # init routines will then automatically figure out the font settings)
         settings = Gtk.Settings.get_default()
+        settings.set_property('gtk-theme-name', 'sugar')
+        settings.set_property('gtk-icon-theme-name', 'sugar')
         settings.set_property('gtk-font-name',
                               '%s %f' % (style.FONT_FACE, style.FONT_SIZE))