Bug 1042319 - [Gallery] Update gallery edit UI r=djf

You might want to ask UX about this. If the user changes to black/white, then back to color, it makes sense to disable the Save button again if there really aren't any edits. But for more complicated edits, if the user completely undoes them they may not realized what they've done and could be confused when the save button gets disabled again. Perhaps we should always just save even if nothing has changed... For now it is an easy way to strip geo tags from a photo :-)