Merge pull request #2868 from kubikrubikvkube/master

Functional interfaces annotation and bugfixes

Mage.Client/src/main/java/mage/client/util/Command.java

@@ -3,7 +3,7 @@ package mage.client.util;
 /**
  * @author nantuko
  */
+@FunctionalInterface
 public interface Command {
-
     void execute();
 }

Mage.Client/src/main/java/mage/client/util/Listener.java

@@ -34,6 +34,7 @@ import java.io.Serializable;
  * @author BetaSteward_at_googlemail.com
  * @param <E>
  */
+@FunctionalInterface
 public interface Listener<E extends Event> extends Serializable {
 
     void event(E event);