title: Add dataProcessor to ckeditor yaml configuration in TYPO3
body: <p>I'm wondering how to add a rule to the dataProcessor like it was possible in the old htmlarea.</p>
  
  <p>In my case I want to add a fixed class to the "ul"-tag.</p>
  
  <p>I tried something like that (tried to adapt the js configuration from ckeditor)</p>
  
  <pre><code>editor:
     config:
        format_p:
          - { element : 'p', attributes : { 'class' : 'ul' }}
  </code></pre>
  
  <p>...but it does not work.</p>