panel: Start the status area before extensions are loaded

The order of indicators depends on the order of calls to
Panel.addToStatusArea. To have it consistent across enabling and
disabling of extensions, we need to place the core ones first.

https://bugzilla.gnome.org/show_bug.cgi?id=653205

js/ui/main.js

@@ -149,6 +149,7 @@ function start() {
     layoutManager.init();
     overview.init();
     statusIconDispatcher.start(messageTray.actor);
+    panel.startStatusArea();
 
     _startDate = new Date();
 
@@ -188,7 +189,6 @@ function start() {
     ExtensionSystem.init();
     ExtensionSystem.loadExtensions();
 
-    panel.startStatusArea();
     panel.startupAnimation();
 
     global.display.connect('overlay-key', Lang.bind(overview, overview.toggle));