Scale images.

Image mummifiers need the ability to scale images if they are beyond some configurable threshold.

A user will likely want to dump a bunch of full-size, original images into the source tree without bothering to individually scale or otherwise manipulate them. But they probably don't want the full-size image being deployed to the size, primarily because of file size. Thus there needs to be some configurable threshold, probably based on file size, above which the image mummifier would automatically scale the image.