Add simple text field question.

A precursor to [this story](https://www.agileplannerapp.com/boards/105200/cards/5222), adds a simple text field question to smart-answers using [Smartdown](https://github.com/alphagov/smartdown).

I don't think this is a multiple choice question anymore? Is there any chance we can the text question as an integration test while maintaining all the existing questions in the animal flow?