alternate file/image change view

[benzkji]

Goals

• clearly show that one can replace existing files.
• allow to rename a file (without re-uploading), by showing the field original_filename (needs some validation/prevent extension change!?)
• make the user widget a dropdown
• think about what name is intended for? drop it?

Fields

• full version: file, caption, description, alt_text, author / advanced: subject_location, user, sha1, canonical_url
• reduced version : - file, author / advanced: subject_location, user, sha1, canonical_url

Input

django-cms/django-filer#835