text: Title: Image uploading and updating is not working with django-filer
  Body: I have integrated django-jet for all it's beautiful design and customized functionalities.
  I'm also using django-filer for file and image uploading.
  But I'm facing this issue when using djang-filer with django-jet. 
  -
  
  >  I'm unable to change image after uploading it for the first time. Image upload popup is also not opening.
  Simply, I can select the image for upload for the first time but after that I can not update that image.
  
  Please check below screenshot.
  ![screenshot](https://cloud.githubusercontent.com/assets/6413205/26345692/4e4abc7a-3fc1-11e7-9c83-d4a9f660cbb9.png)
  
  Has anybody encountered same problem? Help me.