(enhancement) remember to allow "Download images" for a given sender

If an HTML message has images, you have to explicitly "Download images" to see them. However, this is not remembered outside the current session, and even then, only for that message, not for the sender. It would be convenient to also have an option to remember that permission for a given sender. Options are to have two buttons ("Download images", "Always download images for this sender") or to replace the "Download images" with "Always download images for this sender" after clicking)