Include domain in rational expression question

I've added a new solution box to the question whenever you divide by an expression so you have to include the domain condition as part of your answer.

It's formatted using a table isn't isn't ideal especially as tabbing from one box to another goes in an unintuitive order, but it seemed better than creating a lot more divs and trying to line them up.

I still can't get rid of the old merge as part of my pull request.