Move the subscription to LocationChanged and Deactivated Window events to OnLoaded.

When you have one single WPF Window and its Content is a WebView, you could simulate reloading of the WebView, by disposing the old one and creating a new one. This causes the
```OnVisualParentChanged``` to execute two times, for the old and new WebView. The Window is the same so the following code,  
```window->LocationChanged += _handler;
window->Deactivated += _handler;``` 
executes two times. When the location of the Window changes the handler for the old, disposed view is invoked, which is incorrect and causes exceptions.