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

js/ui/sessionMode.js

@@ -138,7 +138,7 @@ function _loadModes() {
 
 function listModes() {
     _loadModes();
-    let id = Mainloop.idle_add(function() {
+    let id = Mainloop.idle_add(() => {
         let names = Object.getOwnPropertyNames(_modes);
         for (let i = 0; i < names.length; i++)
             if (_modes[names[i]].isPrimary)