Deal with BC Break in the Prismic API

Ref: https://github.com/netglue/prismic-client/pull/366

A new field has been added to the shape of images in the response called `edit` - this breaks the client because it expects the `edit` field to be an image view or thumbnail.

A fix is already implemented, but this edit property needs to be dealt with properly and we need new fixtures and tests for it.