NotesManager fires events instead of executing a callback.
NotesManager has an internal state, and reports the load error as an event.
ManifestFile now reports errors.
NotesManager exposes the state and model properties.
Refactored 'state' to 'internalState' because it conflicts with a Y.Base private property.
NotesModel can be accessed only through NotesManager.
NoteView uses NotesManager to access the note and to display status messages.