Problem correctness / incorrectness icon unintuitive

[artasparks]

There are several problems that have been highlighted with the problem icon. I think generally, it's a little unintuitive because

• The correctness icon isn't an icon you can interact with.
• It's in a rather somewhat unexpected location.

I think maybe the right way to go is to ditch the icon and flash a check-mark or x-mark across the screen when users get the problem right/wrong. This is a little tricky to do right, because it has the potential to be jarring.