Hook up display of grade files ready for download to new instructor dashboard.
Add grade calculations button to new instructor dashboard.
Add support for running grades and pushing directly to S3 from the new instructor dashboard
Minor tweak to new instructor dashboard display of grade download, removing some old commented out HTML
PEP8 cleanup, remove unnecessary inner class
UX for Data Download tab on instructor dash
Restrict grade downloads to edX superusers
Instructor dashboard UX and code cleanup
Respond to PR comments, add docstrings and comments.