[Splitting https://tickets.metabrainz.org/browse/CAA-96]

It'd be nice to add a way store how much processing an image has undergone. Among other things, it could be used by Picard to decide which artwork to embed. I think a few levels would be fine:

• (blank)/unspecified/unknown
• raw — as close as you can get to the data spit out by the image sensor. Cropping out background OK (i.e., crop to item borders—not changing the item shape), maybe rotation, not much else.
• corrected — applying color profile, manual color correction, perspective correction, etc.; should not introduce artifacts
• minimal — descreen, damage repair, etc. that is intended to make it look right — may however introduce artifacts.
• edited — anything more, e.g., making a square version. Should still represent the release it's uploaded too, of course.

For some formats (when CAA supports them, which is not yet), it'd be nice to auto-select a default based on the format. E.g., DNG would auto-select raw.