make alertify display time configurable

customize.dist/application_config.js

@@ -6,5 +6,11 @@ define(function() {
      */
     config.availablePadTypes = ['pad', 'code', 'slide', 'poll'];
 
+    /*  Cryptpad apps use a common API to display notifications to users
+     *  by default, notifications are hidden after 5 seconds
+     *  You can change their duration here (measured in milliseconds)
+     */
+    config.notificationTimeout = 5000;
+
     return config;
 });