"Cropped" image URL not present in /posts endpoint.

[KriskotooBG]

The "Cropped" version of a post is not avaiable on the posts api endpoint. (https://static1.e621.net/data/crop/aa/bb/aabbcc...) It is used for the mobile view, but doesn't seem to be included in the result set.

It would be nice to either get it, or a flag saying if a cropped image is avaiable or not, as some posts don't seem to have that version.

[Sindrake]

Alternatively, we could just phase out the cropped versions entirely.