HOTFIX: Variant Images Supported In Google Product Feed

Variant images are now supported in google feed, so if the variant has an image assigned to it that will be used as the primary image in the feed, and if the product contains a main product image it is appended to the additional_image_link field.

Also created AC.ACS.Catalog.Helpers.CatalogHelper.GetProductImageUrl helper which allows you to pass in a variant ID to use in place of the main product image.