Update Model and ModelManager

[CornCobs]

HireLah! has a totally different model from AddressBook, thus Model needs to change.
Specifically, it needs to:

1. Contain IntervieweeList, AttributeList, QuestionList and Metrics
2. Provide a finalize method which when called, makes AttributeList and QuestionList unmodifiable (Should add a boolean flag to these classes)
3. Contain a mode flag which indicates which mode the app is in, affecting the types of commands that can be given. Modes are Normal mode and interviewing mode

Implementation wise, I think it is ok for ModelManager to simply expose the components, so Commands execute on the components themselves rather than through wrapper methods exposed by Model

[bscrow]

Resolved in #57