New css class for answers

A class "correct" or "incorrect" for each answer. To visualy point out
the answer status in quizResults to give the user a chance to learn
right answers and then run the test again.

Additionaly a class incorrectResponse as pendant to correctResponse.

See #43
Merge branch 'answer-status-css-class' of github.com:Aybee/SlickQuiz into Aybee-answer-status-css-class
moved answer correct/incorrect classes to checkAnswer method to make it harder to cheat
Merge branch 'Aybee-answer-status-css-class'