title: Wicket ImageResourceReference ist mounted multiple times everytime the page is reloaded
body: <p>I'm trying to mount an ImageResourceReference on my Page, but the ExternalLink is mounted multiple times (everytime I reload the page, I get a new additional link (same one).
  For example when I start the server and load the page for the first time, there's just one ExternalLink, the second time, two links, third time three, etc... </p>
  
  <p>What could be the reason for that? </p>
  
  <p>Here is my code: 
  WebApp.java:</p>
  
  <pre><code>void init() {
  .....
  mountResource("/book/number/${number}/images/ray/${name}", new ImageResourceReference());
  ....
  }
  </code></pre>
  
  <p>ImageResourcesPanel:</p>
  
  <pre><code>public class ImageResourcesPanel extends Panel {
  
      private static final long serialVersionUID = -8723530004274531683L;
      private static Logger logger = LoggerFactory.getLogger(ImageResourcesPanel.class
              .getName());
  
      /**
       * The image names for which dynamic images will be generated
       */
      private static List&lt;String&gt; IMAGE_NAMES = new ArrayList&lt;String&gt;(); 
  
  
      public ImageResourcesPanel(final String wicketId, final IModel&lt;Device&gt; model) {
          super(wicketId, model);
  
          String pathToImage = "images";
          IMAGE_NAMES.add(pathToImage);
  
          ListView&lt;String&gt; listView = new ListView&lt;String&gt;("list", IMAGE_NAMES) {
  
              private static final long serialVersionUID = 1L;
  
              @Override
              protected void populateItem(ListItem&lt;String&gt; item) {
  
                  logger.debug("Executed!");
  
                  ResourceReference imagesResourceReference = new ImageResourceReference();
                  PageParameters imageParameters = new PageParameters();
  
  
                  int number = model.getObject().getNumber();
                  String imageName = item.getModelObject();
                  String folder = model.getObject().getLinkToFolder();
                  imageParameters.set("name", imageName);
                  imageParameters.set("number", number);
                  imageParameters.set("folder", folder);
  
                  // generates nice looking url (the mounted one) to the current image
                  CharSequence urlForWordAsImage = getRequestCycle().urlFor(imagesResourceReference, imageParameters);
                  ExternalLink link = new ExternalLink("link", urlForWordAsImage.toString());
                  link.setBody(Model.of(imageName));
                  item.add(link);
  
              }
          };
          add(listView);
      }
  }
  </code></pre>