Fix check box to send appropriate data [#47656837]
Update check_answer to handle multi-answers

[#47656837] This ensures the check-answer script actually sends the selected answers for checkboxes as well as radio buttons.

https://www.pivotaltracker.com/story/show/47656837
Disabling check-answer button for multi-answer MC

[#47656837] The behavior of "Check Answer" for questions with multiple answers is much more complicated than single-answer, and at the moment it's not well defined.

https://www.pivotaltracker.com/story/show/47656837