A Singleton IController implementation.

In PureMVC, the Controller class follows the 'Command and Controller' strategy, and assumes these responsibilities:

• Remembering which ICommands are intended to handle which INotifications.
• Registering itself as an IObserver with the View for each INotification that it has an ICommand mapping for.
• Creating a new instance of the proper ICommand to handle a given INotification when notified by the View.
• Calling the ICommand's execute method, passing in the INotification.

Your application must register ICommands with the Controller. The simplest way is to subclass Facade, and use its initializeController method to add your registrations.