title: Can't use values from App.config file in WPF
body: <p>I added keys with values to my config file and after some web-search i found out how to import those values into my .cs file for later use. 
  At the moment i put the value into the content attribute of a label.</p>
  
  <p>When i run the program the label is empty. That means that something must have happened to it because i statically inserted some text in the XAML.</p>
  
  <p>This is the config:</p>
  
  <pre><code>&lt;configuration&gt;
      &lt;startup&gt; 
          &lt;supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" /&gt;
      &lt;/startup&gt;
      &lt;appSettings&gt;
          &lt;add key="SourcepathClient" value="D:\xxx"/&gt;
          &lt;add key="SourcepathWin32" value="D:\xxx"/&gt;
          &lt;add key="DestinationpathUpdatePackages" value="D:\xxx"/&gt;
          &lt;add key="DestinationpathClient" value="D:\xxx"/&gt;
      &lt;/appSettings&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>and this the .cs file:</p>
  
  <pre><code>private void Window_Loaded_1(object sender, RoutedEventArgs e)
  {
      LabelSourcepath.Content = System.Configuration.ConfigurationManager.AppSettings["SourcepathClient‌​"];
  }
  </code></pre>
  
  <p>I dont get any error, simply the value isnt shown in my label.</p>