Allow Safari desktop notifications.

Apparently the Safari version of requestPermission wants to take
a callback function as an argument and gets unhappy when you
don't give it to them.

I learned this tip from http://www.inserthtml.com/2012/07/html5-app/

But more importantly, from the draft spec at
http://dev.chromium.org/developers/design-documents/desktop-notifications/api-specification
mentions that requestPermission takes a callback function that is
invoked once the user accepts.

(imported from commit c1d98239028ffce2e294568c5711315f985160a3)

zephyr/static/js/notifications.js

@@ -78,7 +78,7 @@ exports.initialize = function () {
             return;
         }
         if (window.webkitNotifications.checkPermission() !== 0) { // 0 is PERMISSION_ALLOWED
-            window.webkitNotifications.requestPermission();
+            window.webkitNotifications.requestPermission(function () {});
             asked_permission_already = true;
         }
     });