Support SceneDelegate based application

[yasheedv]

I have created a sample application with iOS 13 target. It's using SceneDelegate.
PIPKit.show(with: PIPViewController()) not showing the PIPViewController

[yasheedv]

It's working if I change PIPKitWindow allocation like below under PIPKit class line number 73

let newWindow: PIPKitWindow
if let currentWindowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene {
newWindow = PIPKitWindow(windowScene: currentWindowScene)
} else {
newWindow = PIPKitWindow() }

[Kofktu]

Can I request a PR?

[Kofktu]

@yasheedv
Could you test it with that feature/issue-34-support_scenedelegate branch?

[Pobe16]

I tested it today and it is working very good. Please PR