Merge pull request #2 from theonicolaou/version2

Version 2: add client-side validation on radio buttons
Merge pull request #3 from theonicolaou/version2

Version 2: move score feedback if/else statement into own function
(WIP) add Back button functionality
Update README
Move isChecked variable into quizVariables object
Merge pull request #4 from theonicolaou/cleanup

Move isChecked variable into quizVariables object
Fix merge conflicts (backbutton with master)
clean up indentation
(WIP) adjust scoring on selection of duplicate answer - commented out this.storeAnswer in goBack() function
Remove commented code
Merge pull request #5 from theonicolaou/backbutton

Merge WIP backbutton code into version2 branch