Fix images on home, search & cateogry pages: 27444

@prabinv @texasag @kevinsproles & @tsanko for completeness

I added a filter to parse images form the product.imageCollections object.
By default it returns the image for 'default' & 'medium' but that can be overridden with arguments to the filter fn. 
Maybe an refactoring for later, is there a way to get the "no-image" value into the filter, so that the filter doesn't need to know about the theme folder structure? It can be a parameter, but then the caller would need to pass it in every time, and that doesn't look good to me. I think we should have it as a "constant" injected into the filter. What are your thoughts on this?