Merge Branch-Ethan-8-Oct into master

[RCPilot1604]

closes #14

Add the following classes to the project:

1. Assignment //represents an assignment (aka grade)
2. Attendance //represents an instance of attendance taken (at a specific venue and time and for a specific course)
3. Student //represents a student
4. AttendnaceCommand //parent class for all attendance-related commands
5. AssignmentCommand //parent class for all assignment-related commands
6. StudentCommand //parent class for all student-related commands

7-12. Add/Delete Commands (as subclasses) for 4.-5.