title: Tell StormCrawler to delete pages from ES-index after they have been deleted on the server
body: <p>I have the following scenario:</p>
  
  <ul>
  <li>An existing page gets crawled by StormCrawler</li>
  <li>StormCrawler adds a corresponding document to an Elasticsearch index</li>
  <li>The page is deleted on the server</li>
  </ul>
  
  <p>=> The crawler "detects" the removal of the page by updating the status-index: The document gets status "FETCH_ERROR" (and after reaching the "max.fetch.errors" the status "ERROR").</p>
  
  <p>Problem:
  The Elasticsearch-Index still keeps the document, but since the page was deleted that doesn't make sense.</p>
  
  <p>Looking at the configuration, I haven't found a way to tell StormCrawler to remove documents from the ES-index which have status "ERROR" (e. g. have been deleted).
  Is there a way to accomplish this using StormCrawler or is there a reason why this is not possible?</p>
  
  <p>Thank you very much for your help!</p>