Support role-based security

[kcargile]

The system should support a hierarchical user authorization scheme. This should eventually be customizable by the system administrator, but OOB should implement something along these lines:

• Admin: The system administrator. Access to all settings.
• Headmaster: Has autonomy over all training materials. Ability to delegate instructor tasks and manage instructors.
• Instructor: A course author. Has access to create and manage courses, enrollments, etc.
• Student Manager: Has autonomy over a group of students. Can delegate tasks to students, manage them, etc.
• Student: A student. Has the ability to participate in courses in which she is enrolled.