Validate radio button input

[jeff-eng]

• [x] User should not be able to check answers if they don't select an answer for each trivia question.
• [x] Disable the Check Answers button if user has not selected an answer for each question.
• [x] Keep state of whether user has answered all questions or not.

[jeff-eng]

All objectives were completed. Ended up also doing the conditional rendering of correct and incorrect answers which involved passing state from parent on through to grandchildren components.