Add ability to view and submit multiple choice questions in Take Quiz

This needs some more visual refinement, and I still need to add e2e tests. Some usability enhancements on the editing side, like reordering choices and smarter TAB key behavior, would be nice as well.

The viewquestion directive has a couple ugly spots in it right now, like the really long and complicated ng-class expression for the multiple choice buttons, and there's some code duplication with the submit/next buttons. This should be revisited at some point.