title: django multiple select in admin change-list
body: <p>Our product model can have multiple campaigns. Our customers change these campaigns frequently and generally on multiple products. So what we need right now seems that we need to show a multiple select widget on a change-list of Product model where our customers can easily change the campaigns. </p>
  
  <p>Any idea on this? Maybe another way to achieve this kind of UI interaction?</p>
  
  <p>Thanks,</p>