Refactor the "choose resource" button on document editor

The button should be called "Choose an icon"

The popup should be organized like this :

• Upload a new picture (with the upload widget)
• Or select an existing one:
  With a list of the pictures and the display of it in small size
• a Cancel, Select button
  The select either post the uplaoded picture and select it for the document type, or select the selected existing one for the document type.

Also, once a user has uploaded a picture, we should hide the list of existing one to be more consistent