Fix in the repository summary info object (implements IsSerializable)

src/main/java/eu/dnetlib/repo/manager/domain/RepositorySummaryInfo.java

@@ -1,8 +1,10 @@
 package eu.dnetlib.repo.manager.domain;
 
+import com.google.gwt.user.client.rpc.IsSerializable;
+
 import java.util.Date;
 
-public class RepositorySummaryInfo {
+public class RepositorySummaryInfo implements IsSerializable {
 
     String id;
     String repositoryName;