Provide option to save images with messageid as filename

[tehstone]

By saving the images with the message id as the filename, it's simple to guarantee each image will have a unique filename even when combined with images downloaded via other methods. In cases where a single message contains multiple images, append some other number or letter to the filename to differentiate.

[jasonhahm]

I second this. I was thinking of message timestamp for management, but either way would be great options.