title: ckeditor 4 jQuery Adapter, How to add a custom button?
body: <p>code 0:</p>
  
  <pre><code>$editor.ckeditor(function () {
      var editor = this;
      editor.ui.add('MyButton', CKEDITOR.UI_BUTTON, {
          label: 'My Button',
          command: 'test'
      });
  }, {toolbar: [['MyButton']]});
  </code></pre>
  
  <hr>
  
  <p>code 1:</p>
  
  <pre><code>var editor = CKEDITOR.replace('editor', {toolbar: [['MyButton']]});
  editor.ui.add('MyButton', CKEDITOR.UI_BUTTON, {
      label: 'My Button',
      command: 'test'
  });
  </code></pre>
  
  <hr>
  
  <p>[code 1] is OK, normal to show at toolbar, but [code 0] is not work, how to use jQuery Adapter to add custom button??</p>
  
  <hr>
  
  <hr>
  
  <p>updated [code 0]:</p>
  
  <pre><code>$editor.ckeditor(function () {
      var editor = this;
      editor.on('pluginsLoaded', function(event) {
          editor.ui.add('MyButton', CKEDITOR.UI_BUTTON, {
              label: 'My Button',
              command: 'test'
          });
      });
  }, 
   {
      customConfig: '/ckeditor-config.js'
  });
  </code></pre>