WhereOnEarth - Adding end game screen with replay

- Adding ending.png for use as our ‘final’ screen after quiz.
- Created new showEnding method that puts all the visual elements on
our end screen. This will be called when the user completes the quiz.
- This final view also contains a ‘play again’ button so that the user
can redo the quiz.
- Adding global variable endView so we can access this entire view
(with all its child elements).
WhereOnEarth - Quiz View is global variable too

- Renaming method startQuiz to createQuiz
- Adding a global variable to store the UIView containing all the
visual elements of our quiz layout.
- Adding new method replaceViewWithOtherView that does a quick fade
animation.