Product Images and Q&A bottom line now document their full responses

Two V1 responses now match what the API returns.

• Product Images: 10 response fields that weren't documented are now listed. updated_at gives the time each image was last updated. The other nine, such as thumbnail_url and shop_owner, come back as null, so use image_url and original_image_url for image links.
• Retrieve the bottom line for Q&A: the response now has a schema: total_questions and total_answers for the product. An unknown SKU returns 404.