Crop settings should reset when replacing an image

Issue Summary

When I replace an image with an entirely different one, the old crop window stays in place, even though it very likely won't make sense with the new image context. This alone isn't much of a problem, but if the second image is a different size or has very different dimensions, the crop window can get lost. The end user doesn't realize it, because without a visible crop window, there's no indication that anything is wrong.

Instead, I'd say replacing an image should reset the crop window to the dimensions of the new image, as if uploading the image for the first time.