Updated authorization, added utility function

- Added is_student_in_section() function to db1.py
- Moved roles into the auth_group table.
- Added code to automatically populate the auth_group table with default roles.
- Added code to add all users except user 1 to the auth_membership table as student.
- Updated methods in default.py to use the new auth_membership relations.
- Added decorators to methods in default.py to enforce authorization.
- Updated view default/course.html to use the new auth_group.role value, as my updates broke it.
- I tested everything I could think of to make sure everything still works as it did as of the end of class last week.