Pluvo

- add include_answers flag to include answers in the student progress report

- add API view for getting student course sessions

- Add retry delay
- Increase retry count
- Add copy course method

- Allow filtering get_progress_report by completion_date
- Updated requests to 2.20.0

- Add filename arg to get_course_report (19)

- Added `get_course_report` function, This function will request a url to get the report of a course for a specific user. If the report doesn't exists yet it will be start generating it in the background.
- Added delete course test to get 100% test coverage again.