added multiple values on ROOTNode annotation

src/main/java/org/gcube/common/storagehub/model/annotations/RootNode.java

@@ -9,5 +9,5 @@ import java.lang.annotation.Target;
 @Target(ElementType.TYPE)
 public @interface RootNode {
 	
-	String value();
+	String[] value();
 }

src/main/java/org/gcube/common/storagehub/model/items/ExternalLink.java

@@ -14,7 +14,7 @@ import lombok.Setter;
 @AllArgsConstructor
 @Getter
 @Setter
-@RootNode("nthl:ExternalLink")
+@RootNode({"nthl:externalLink","nthl:ExternalLink"})
 public class ExternalLink extends Item{
 		
 	@Attribute("hl:value")