Backport PR #4143: update example custom.js

fix event for at-page-load events use font-awesome icon, not jquery-ui

closes  #3998

IPython/html/static/custom/custom.js

@@ -1,47 +1,49 b''
 // leave at least 2 line with only a star on it below, or doc generation fails
 /**
  *
  *
  * Placeholder for custom user javascript
  * mainly to be overridden in profile/static/custom/custom.js
  * This will always be an empty file in IPython
  *
  * User could add any javascript in the `profile/static/custom/custom.js` file
  * (and should create it if it does not exist).
  * It will be executed by the ipython notebook at load time.
  *
  * Same thing with `profile/static/custom/custom.css` to inject custom css into the notebook.
  *
  * Example :
  *
  * Create a custom button in toolbar that execute `%qtconsole` in kernel
  * and hence open a qtconsole attached to the same kernel as the current notebook
  *
- *    $([IPython.events]).on('notebook_loaded.Notebook', function(){
+ *    $([IPython.events]).on('app_initialized.NotebookApp', function(){
  *        IPython.toolbar.add_buttons_group([
  *            {
  *                 'label'   : 'run qtconsole',
- *                 'icon'    : 'ui-icon-calculator', // select your icon from http://jqueryui.com/themeroller/
- *                 'callback': function(){IPython.notebook.kernel.execute('%qtconsole')}
+ *                 'icon'    : 'icon-terminal', // select your icon from http://fortawesome.github.io/Font-Awesome/icons
+ *                 'callback': function () {
+ *                     IPython.notebook.kernel.execute('%qtconsole')
+ *                 }
  *            }
  *            // add more button here if needed.
  *            ]);
  *    });
  *
  * Example :
  *
  *  Use `jQuery.getScript(url [, success(script, textStatus, jqXHR)] );`
  *  to load custom script into the notebook.
  *
  *    // to load the metadata ui extension example.
  *    $.getScript('/static/notebook/js/celltoolbarpresets/example.js');
  *    // or
  *    // to load the metadata ui extension to control slideshow mode / reveal js for nbconvert
  *    $.getScript('/static/notebook/js/celltoolbarpresets/slideshow.js');
  *
  *
  * @module IPython
  * @namespace IPython
  * @class customjs
  * @static
  */