[editing] module no longer depends on PIL, remove unused 'out'

This was used for converting cover art images to JPEG, but is no longer
needed as of commit f487e39bf58cc171b5a460d11b9cbc76b53b97a8
[editing] Use integer division
[editing] Use imghdr to detect image type, extension may be unreliable

Per request from nikki: "bandcamp definitely has had pngs in past
sometimes with a .jpg extention"