FIXED rotation issue

In case the app was forcing an interface orientation (e.g. UIInterfaceOrientationMaskPortrait in supportedInterfaceOrientations), the status bar was still rotating as the RootViewController of the OverlayWindow wasn't enforcing any orientation. This could be "fixed" by removing this controller.

The resulting warning "Application windows are expected to have a root view controller at the end of application launch" on app launch is avoided by moving window creation into getter.

I've tested this on iOS 7 and iOS 8 (DP1).