Adding e2e tests for multiple choice questions in Take Quiz

TO DO: e2e tests for *editing* multiple choice questions. (Quiz editor tests are currently failing.)
Update quiz editor tests for multiple choice questions

Also removed the explicit .then() calls since WebDriverJs takes care of resolving promises.

There is one failing test case at the moment related to adding a new question using the TAB key. I will fix this one later as I'll be tweaking this feature later (you can't add a new question using the TAB key from a multiple choice question, and I'm not sure if we really want that). I will come back to this test case and either update or delete it at that time.