Should be added as a subview of key window

[radutzan]

Currently, -show adds the view as a subview of the rootViewController of the window, or to the presentedViewController if there's one, which is good enough for most cases.

[radutzan]

Please note that after this change, OLGhostAlertView has to be shown in or after viewDidAppear: is invoked on the Root View Controller. If you attempt to call show before that, the instance may not be visible on the screen.