[React] Incorporate network-aware code-splitting into Shrine

[addyosmani]

The originally React Shrine application implemented code-splitting for a number of views. We could augment the implementation there to use network-aware code-splitting such that:

• For a product page, a user is displayed an item with an image
• If you're on a slow-connection you are shown just an image with the ability to view it. We only load the smallest version of this component possible.
• If you're on a fast-connection, we conditionally load a version of the product image with react-magnifier support. This allows the user to get an enhanced experience. Basically, they can magnify the image to view more details on it.

Assigned to Anton