Rewrite the Grade Book application

[DavidWhitlock]

Now that I've gain all of this experience writing Swing apps using MVP (issue #99), I think I should rewrite the Grade Book application to follow the same patterns (and use some of the same code). I think it would make an interesting screencast.

• Refactor GradeBookGUI into several pieces
  • Logic for maintaining recently loaded grade books (an MVP)
  • The menu
  • The toolbar
  • The status display (an MVP)
  • Leverage existing MVPs from the POA program