Move image upload to create badge form

What do you think of improving UX by adding image upload to the create badge form? The image would be saved in the library upon badge creation, and we would still have our library.

The image upload form in Image tab currently requires two submission (one for ajax upload, and one for confirmation), this is not user friendly and it should be removed (or replace by a help message).

See also #1537138: Images upload form not working