Added a Refresh button to ImageReaders

I was playing with it not forcing, and noticed that occasionally I hit refresh, but the image didn't update. I'm guess maybe that happens when you write the image twice within a very short timespan, and the file stats show the same data? Maybe that wouldn't come up in a real world case, but it was frustrating to hit refresh and see nothing, so I went for over cautiousness instead of potential user distrust... I don't mind changing it though if you prefer.