use alertify instead of browser prompt

www/whiteboard/index.html

@@ -4,6 +4,7 @@
     <meta content="text/html; charset=utf-8" http-equiv="content-type"/>
     <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
     <script data-bootload="main.js" data-main="/common/boot.js" src="/bower_components/requirejs/require.js"></script>
+    <link rel="stylesheet" href="/customize/main.css" />
     <style>
         html, body{
             padding: 0px;