* still needs to support uploading a list
* also want to clean up and refactor the code a bit

* add a days_early_for_beta inherited policy option
* students in the beta_testers_{COURSE} group get to see content that many days early
* Clean up some docstrings related to time formats
* Add basic test

remove try...except workaround for circular import bug fixed by https://github.com/MITx/mitx/issues/1260

Make LMS access depend on which course run the access is occurring in, so that permissions can be based on the course run, rather than the whole course

Switch to using staff group names that are only specified by org/course, rather than the full course_id

respond to Cale pull request comments. Update access.py (LMS) to use the same 'check for legacy group name first' logic. Add SECRET_KEY setting to the CAS project so that auth tokens from CAS are accepted in the LMS

- triggered by anon users when all courses have started (or start dates are off).

functionality - grade dump and download as csv, manage staff list,
force reload of course from xml

* if error is in xmodule_constructor(), catch and return an ErrorModule
* if error is somewhere else in get_module(), return None

* Save errors for courses that failed to load in modulestore
* global staff can see course errors on their dashboard
* put policy loading errors into the error trackers
* add has_access(user, 'global', 'staff'), which is equiv to user.is_staff for now

Added styles to grade out the top and bottom of the sidebar border and fixed spacing with the video and the sequence nav

- don't call has_access directly from template, pass a staff_access variable instead

* error modules now hidden via access control
* get_module() returns None if user doesn't have access