Add methods for choice of returning with or without response.

This commit adds a method to return with a response, and a method to
return without of a response so it can be used with other handlers. This allows the command using image to return it's expected output without additionally outputting the image result.
Calling this `fetch_with_response` is a bit confusing since `response` has two different meanings in this context. Would it make sense to call these `fetch_with_reply` and `fetch_without_reply`?