Build a simple grade book using a versatile data structure. The grade book program should display a menu with the following options

1. Add a new course

2. Add a new student

3. Add a student to a course

4. Add grades for a student in a course

5. Print a list of all courses

6. Print a list of all students

7. Print a list of all students in a course

8. Compute the average for a student in a course

9. Exit