adding new image files for checks and an X
adding classes for <i> tags to deal with the new images
replacing the old checks with the new, adding minor logic to determine what is shown
removing previous answers when updating a fillin
adding support for showing answers as well as responses...
added the 'correct answer' view for fillins and numerical
removing unit test for gradeQuiz temporarily
Merge pull request #144 from Harvard-ATG/feature-139

Feature 139 - closes #139 (for now)