Display product images on Product List and Fulfillment screens

[bummytime]

Inspired by the work in woocommerce/woocommerce-android#875 I realized that we only display product images in the Dashboard→Top Performers VC:

However in ProductListViewController and FulfillViewController we have product placeholders:

Let's see if we can lazily load the images on these 2 screens just like we do on top performers. 😄

[mindgraffiti]

This task requires backend work done before images can be displayed. Putting it back in favor of #764.

[bummytime]

Just a quick reminder that we will need #818 in place before we can address this issue. 😄