Add Exam and Answer models to track scores on quizzes.
Add method to update Answer object with JSON
Add button listener for wrong button.  Use a POST request to find_or_initialize answers as some browsers don't understand PUT requests
When answer is submitted, hide buttons and replace table cell with a unicode character to indicate if the answer was correct or incorrect
Add unicode checkmark or cross for in-progress exams
Add CSS to unicode characters that represent correct and incorrect answers
Add button and ajax method to grade an exam
Add modal to display exam results after exam is graded
Add authorization to API methods used to create Answer and Exam records
Properly implement CanCan for Quiz#show page
Use 'correct' and 'incorrect' instead of 'right' and 'wrong' in the code for consistency
Remove 'failure' alerts when ajax calls are unsuccessful