Combined Listings: Add support for Shopify's combined listings#378

Now that Shopify is offering Combined Listings, (://apps.shopify.com/combined-listings), it would be great if we could use this new technology with our Stiletto theme. This gives a “parent” product for “sibling” products. So, for example, Polo Shirts would be the parent, and then the siblings would be red polo shirt, black polo shirt, etc. You could have a collection of just the parent products where you can scroll through the images of the different colors. Hope I explained this in a way that makes sense.