Add Open Url to Navigation

[nickrandolph]

Open Url should open the specified url in either the external browser, or a webview within the context of the application.

This could be used to display content such as a PDF without having to rely on third party libraries

[rkeithhill-keysight]

I found that this API also works on Linux. Have not tried macOS yet.

Windows.System.Launcher.LaunchUriAsync(new Uri("http://www.microsoft.com"));