Fix config binding for unread status manager.

I broke it in my interface-extraction shennanigans.

Closes DMDirc/Plugins#509

src/main/java/com/dmdirc/FrameContainer.java

         this.eventBus = eventBus;
         this.unreadStatusManager = new UnreadStatusManagerImpl(this);
         this.eventBus.subscribe(unreadStatusManager);
-        configManager.getBinder().bind(unreadStatusManager, UnreadStatusManager.class);
+        configManager.getBinder().bind(unreadStatusManager, UnreadStatusManagerImpl.class);
 
         setIcon(icon);
     }