Second Cover image for Root Theme Catalog

Now we can select one image for the Book Cover, but what is a good book cover picture is not a good image for the catalog.

We need a new field for uploading a picture for the catalog inside of the Cover Metabox of Book Info.

The same aspect ratio (in order to make possible to use the same) but much more litle recommended dimensions (like 1/2 or 1/3 or even 1/4)