title: add multiple extra plugins on a toolbar of ckeditor
body: <p>I want to add multiple plugins(which i have created) on a toolbar of ckeditor. I have written below code in config.js</p>
  
  <pre><code>CKEDITOR.editorConfig = function( config ) {
      config.toolbar_Full =  [
          ['Styles', 'Bold', 'Italic', 'Underline', 'SpellChecker', 'Scayt', '-', 'NumberedList', 'BulletedList'],
          ['Link', 'Unlink'], ['Undo', 'Redo', '-', 'SelectAll'], '/', ['timestamp', '-', 'linkbutton']
      ];
      config.extraPlugins = 'linkbutton, timestamp';
  };
  </code></pre>
  
  <p>and i have two different custom plugins. but another plugin is not accepted. How to add another plugin on a one toolbar?</p>