In which we add multiple choice questions to our supported question types

- Allow creation of questions with type 'multiple_choice'
- Allow manipulation of answers associated with a multiple choice question
- Add multiple choice answers to the question representation
- Allow answers to multiple choice questions to be submitted
- Allow a question_group to be set on questions
- Allow filtering by question_group when listing questions on a quest

@maiamcguinness @thcrock @malynda @wilhow @bunnyblanco