There can be only one WindowFlashingManager!!!

Change-Id: I7a0866b87c71e8251aa5cba5fd227fe7dbed941e
Reviewed-on: http://gerrit.dmdirc.com/4014
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

windowflashing/src/com/dmdirc/addons/windowflashing/WindowFlashingManager.java

 import com.dmdirc.interfaces.config.AggregateConfigProvider;
 
 import javax.inject.Inject;
+import javax.inject.Singleton;
 
 import com.sun.jna.Native;
 import com.sun.jna.NativeLibrary;
 import com.sun.jna.platform.win32.WinUser;
 import net.engio.mbassy.listener.Handler;
 
+@Singleton
 public class WindowFlashingManager {
 
     /** Swing main frame. */