The edit button on gallery MCE views will open a new instance of the media modal. Images can be removed, uploaded, and reordered. However, the "Add images from media library" button is not yet functional.
see #21390, #21809, #21815.
git-svn-id: https://develop.svn.wordpress.org/trunk@22155 602fd350-edb4-49c9-b593-d223f7449a82