title: Send confirmation email when changing the email in Django
body: <p>I'm currently using <code>django-registration</code>, and it is working well (with some tricks). When the user registers, he has to check his/her mail and click on the activation link. That's fine, but...</p>
  
  <p>What if the user changes the email? I would like to send him/her an email in order to confirm that he is the owner of the email address...</p>
  
  <p>Is there an application, snippet, or something <strong>that would save me the time of writing it by myself</strong>?</p>