Move rendering into st-theme-node-drawing.c

The idea behind this move is that we have a lot more control over
rendering if StWidget isn't a big pile of actors, and things are
more efficient.

https://bugzilla.gnome.org/show_bug.cgi?id=607500

src/st/st-theme-node.h

@@ -171,6 +171,11 @@ void st_theme_node_get_content_box         (StThemeNode        *node,
 gboolean st_theme_node_geometry_equal (StThemeNode *node,
                                        StThemeNode *other);
 
+void st_theme_node_paint (StThemeNode            *node,
+                          const ClutterActorBox  *box,
+                          guint8                  paint_opacity);
+
+
 G_END_DECLS
 
 #endif /* __ST_THEME_NODE_H__ */