Implements the random button (which exists on the xkcd homepage) on the "what if" section of xkcd.
Update (v1.0.1): Fixes a bug which caused the references to become unclickable. Thanks to Reddit user /u/Notagtipsy for pointing this out.
Update (v2.0.0): Improves efficiency: a random comic will only be requested if the button is clicked. This is similar to the xkcd random button. Also, I added an icon derived from the "What If?" logo!
Update (v2.0.1): Fixed bug that made the random button always point to the current comic under some conditions.