Legacy dash cleanup

This PR updates the legacy dashboard by removing all buttons and features that are present on the Instructor Dashboard. The advantage of this PR is making very clear upon inspection what few remaining features need to be ported to the Instructor Dashboard. As follow on pull requests, I would like to encourage those using the few remaining features to submit PRs porting the buttons to the new dashboard and deprecating the functions Legacy Dash in the same way done in this PR.

This also removes a lot of unstable and untested code, which is good for the health of our codebase.

I've added a deprecated class to the dash CSS so we can stylize messages as we see fit.

Screenshots of each Legacy Instructor Dashboard section are here: https://drive.google.com/a/edx.org/folderview?id=0B0jBaSRrrplqU3phdGo1dTZjbGM&usp=drive_web
Combine into one message (even though slightly different areas?)
"To manage beta tester roles and cohort groups, visit the Membership section of the Instructor Dashboard"