Clear status when showing a new window.

ui_swing/src/com/dmdirc/addons/ui_swing/MainFrame.java

         if (activeFrame.isPresent()) {
             framePanel.add(activeFrame.get().getDisplayFrame(), "grow");
             setTitle(activeFrame.get().getContainer().getTitle());
+            activeFrame.get().getContainer().getUnreadStatusManager().clearStatus();
         } else {
             framePanel.add(new JPanel(), "grow");
             setTitle(null);