Emphasize UIApplicationDelegate protocol requirements

[benjohnde]

Adjust sample project to emphasize UIApplicationDelegate protocol requirements.

In the current example project window is defined as:

  let window = UIWindow()

If I am using some libraries like SVProgressHUD which access the current UIWindow via the following selector UIApplication.shared.delegate?.window they all crash as this invocation returns nil.

Hence, I propose to update the sample project to meet those protocol requirements.

[dfed]

It's up to adopting applications to declare a window property and feed it to the setup(mainWindow: UIWindow) method on SuperDelegate, but this feels like a reasonable change since we could be leading people towards some pain.