WIP Hh accept answer

Currently the accept action in the answers list-item controller is not persisting the updated value for `accepted` to the DB.
I thought using `if: :accepted` would mean that a question can only have one answer where `accepted` is true, but many where `accepted` is false: http://stackoverflow.com/questions/19575336/rails-custom-validation-only-one-record-can-be-true

Is that not right?

If we wanted a question to `have_one :accepted_answer`, does that mean creating an `accepted_answers` join table/model?