Taking Ike's delete-student-state-for-problem code and putting it in a separate PR so it's not bundled with more debated features.

- lets user see and add cohorts
- needs styling
- needs to allow them to actually manage membership!

Replace all calls to analytics service to use the get methods (pulls from mongodb). Added error handling.

Added instructor tools for resetting attempts on a single student's problem to 0 and for getting student's progress page

remaining:
 * support putting multiple names / emails in the big box we now have

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

Implemented 3 analytics to the instructor dashboard: StudentsEnrolled, StudentsPerHomework, DailyActivityAnalyzer.

Added analytics tab in instructor dashbaord, and call to the analytics back-end to display sample data.

also show pid in migration and instructor dashboard views for thread debugging

- on first visit to courseware, go straight to first section of first chapter
- after, clicking on courseware tab sends you most recent chapter, with a link to the most recent section
  (not to section because that might be confusing, and you might want to do something else (e.g. do homework instead of watch videos)
- Moved course errors into instructor tab.