title: Add custom button to django cms ckeditor
body: <p>I want to add some additional buttons to django-cms-ckeditor, so I read manual and add plugin to ckeditor folder and config.js, after that I saw them from sample html of cKeditor. But I can't make that button appear in django cms editing window.</p>
  
  <p>I added this to my settings.py, where 'Abbr' is my button, but I still see all buttons except mine.</p>
  
  <pre><code>  CKEDITOR_SETTINGS = {
      'toolbar_CMS':[[ 'Image', 'Flash', 'Table', 'HorizontalRule','Smiley', 'SpecialChar', 'PageBreak', 'Iframe', 'Abbr' ] },],
  </code></pre>