cleanup: Use arrow notation for anonymous functions

Arrow notation is great, use it consistently through-out the code base
to bind `this` to anonymous functions, replacing the more overbose
Lang.bind(this, function() {}).

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/23

tests/testcommon/ui.js

@@ -25,7 +25,7 @@ function init(stage) {
 
 function main(stage) {
     stage.show();
-    stage.connect('destroy', function() {
+    stage.connect('destroy', () => {
         Clutter.main_quit();
     });
     Clutter.main();