Retrieves the login status for the user.
This will automatically log the user into your app and return an access token for your app. The user must be logged into Facebook on the device and must have previously logged into your app. The user will be shown a notification stating that the user has been logged in to your app.
public static void RetrieveLoginStatus( FacebookDelegate<ILoginStatusResult> callback )
A delegate that will be called with the login status result.