Merge pull request #369 from Fredasaurus/8-25

scroll, taking out modal scrolling, summary menu, general positioning
rolling back 45ed6e01b4 hopefully more effectively
4 scenario error messages for https://www.pivotaltracker.com/story/show/77686530
back nav item, quiz summary heading
don't hover effect on feedback answer choices
errors when students try to go back and resubmit
better terp error pages
fix for email confirmation problems
minor error message changes
change for making scrollbar visible