Fix EditorPage initial state to have an answerArea instead of answer
Fix EditorPage initial state to have an answerArea instead of answer

When we renamed answer to answerArea this one didn't get changed - we also
weren't passing in the itemDataVersion when the developer JSON mode was enabled
in Perseus One. This picks out the correct props and passes them to JsonEditor.

Fixes https://app.asana.com/0/27216215224639/42168723328067

Test Plan:
Open [a perseus one item](http://localhost:8080/puppies/arias-playground/e/aria-test/edit/x3b5f8843fb8a1d71)
Enable developer JSON mode
Switch items
See 'answerArea' and 'itemDataVersion' in the JSON and no 'answer'

Auditors: aria

abe4mvp/perseus,ariabuckles/perseus,alexristich/perseus,daukantas/perseus,abe4mvp/perseus,ariabuckles/perseus,daukantas/perseus,sachgits/perseus,sachgits/perseus,ariabuckles/perseus,learningequality/perseus,iamchenxin/perseus,ariabuckles/perseus,iamchenxin/perseus,learningequality/perseus,alexristich/perseus