Small refactoring of the notes references to mark the type of the object.
Mock the ManifestCache so we can test.
NoteManager first looks for note info inside ManifestCache.
If this fails, then it reads the note from Dropbox.
Small cleanup.
Renamed ManifestCache to NotesInfoCache.
Created a NotesCache class that controls the access to the cached notes.
Modified the NotesManager and the NoteView to use the new NotesCache.