ContextWindow: Use Task.Run to load data outside main thread

Elwig/Windows/MainWindow.xaml

@@ -5,7 +5,7 @@
         xmlns:local="clr-namespace:Elwig.Windows"
         xmlns:ctrl="clr-namespace:Elwig.Controls"
         Title="Elwig" Height="390" Width="520" ResizeMode="CanMinimize"
-        Loaded="Window_Loaded" Closing="Window_Closing">
+        Closing="Window_Closing">
     <Window.Resources>
         <Style TargetType="Button">
             <Setter Property="VerticalAlignment" Value="Top"/>