Create Rules/checks for changing attendance

[mcflyhalf]

Include a new concept of rules that can be added to attendance manipulation (probably in ModuleAttendance class).

This concept should allow the class (or different objects of the class) to have relevant rules for changing attendance e.g.

• Attendance can only be changed by student agent during class time
• Attendance cannot be marked before the class time
• Certain agents can only mark attendance in certain rooms

This will allow for options to be editted by admin

[mcflyhalf]

These rules should probably be set in the agents themselves so that the ModuleAttendance class only deals with the raw representation of attendance