One checkbox you thought worked but didn't!

Summary:
The radio relies on being passed problemNum as the second
parameter to it's prop `transform` function, but the
answerAreaRenderer wasn't passing the problemNum parameter.

This diff refactors that code a little bit so that it goes
through the same code path that the ordinary renderer uses.

Coming up with these titles is hard.

Test Plan:
Reload
[this item](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%22%2C%22images%22%3A%7B%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fda8df81c78b22f5c69d477d8eabfb583968eaf84.png%22%3A%7B%22width%22%3A400%2C%22height%22%3A70%7D%2C%22https%3A%2F%2Fka-perseus-graphie.s3.amazonaws.com%2Fb59fc02ca1aae800977b8793ed22f647a1aa75ee.png%22%3A%7B%22width%22%3A425%2C%22height%22%3A150%7D%7D%2C%22widgets%22%3A%7B%7D%7D%2C%22answerArea%22%3A%7B%22type%22%3A%22radio%22%2C%22options%22%3A%7B%22choices%22%3A%5B%7B%22content%22%3A%22A%22%7D%2C%7B%22content%22%3A%22B%22%7D%2C%7B%22content%22%3A%22C%22%7D%2C%7B%22content%22%3A%22D%22%7D%5D%2C%22randomize%22%3Atrue%2C%22multipleSelect%22%3Afalse%2C%22displayCount%22%3Anull%2C%22noneOfTheAbove%22%3Afalse%2C%22onePerLine%22%3Atrue%7D%2C%22calculator%22%3Afalse%7D%2C%22itemDataVersion%22%3A%7B%22major%22%3A0%2C%22minor%22%3A1%7D%2C%22hints%22%3A%5B%5D%7D)
Over and over and see that the radio options reload in
different orders.

Auditors: alex

Subscribers: pamela