Allow User to Assign a Game Controller Button as a Screenshot Capture Key

This, again, would be a convenient way for me to play on my Dolphin emulator. I like taking screenshots on the Dolphin emulator, and it's a pain trying to take a screenshot while I play the game, as I have to go from my game controller to a computer key, which is inconsistent for me.

If anyone could fix this problem, that would be great. :)