Window Owner isn't set

[dukedvl]

when creating a new "NotificationsOverlayWindow", in the NotificationManager, the window's owner is unset..

Creating toast notifications using the method below, will always leave the ToastWindow open as the application closes.

var notification= new NotificationContent(){ .. };
manager.Show(notification);

_window.Owner being set inside the NotificationManager allows normal Dispose/Close methods to end the lifecycle with the program, as WPF defaults to only closing on "LastWindowClosed".. this will confuse a lot of consumers of the NuGet Pkg...