title: Sonata media bundle - get pdf file by name or change filename on update
body: <p>I currently use SonataAdminBundle and SonataMediaBundle.<br>
  I have a problem with the media bundle files because my pdf file is not saved with its name but with md5 or another format.</p>
  
  <p>For example:</p>
  
  <ul>
  <li>media table</li>
  <li>id : 1</li>
  <li>name : iphone.pdf</li>
  <li>provider_reference : 9a0b7a35131e23f91666324562c52f08b7cb6604.pdf</li>
  </ul>
  
  <p>I don't want to get my pdf by this:</p>
  
  <pre><code>9a0b7a35131e23f91666324562c52f08b7cb6604.pdf
  </code></pre>
  
  <p>but with its name ( <code>iphone.pdf</code> ).</p>
  
  <p>I want to know if it's possible to:</p>
  
  <ul>
  <li>get the pdf file by name?</li>
  </ul>
  
  <p>or</p>
  
  <ul>
  <li>save my pdf file with a particular name?</li>
  </ul>