Fix ClassCastException on EffortDurationBox

It only happens with ZK5. Marshal and unmarshal are needed.

FEA: ItEr75S08MigrationZK5

navalplanner-webapp/src/main/java/org/navalplanner/web/common/EffortDurationBox.java

@@ -31,6 +31,21 @@ public class EffortDurationBox extends Textbox {
         return (EffortDuration) getTargetValue();
     }
 
+    @Override
+    protected Object marshall(Object value) {
+        return coerceToString(value);
+    }
+
+    @Override
+    protected Object unmarshall(Object value) {
+        EffortDuration result = EffortDuration
+                .parseFromFormattedString((String) value);
+        if (result == null) {
+            return EffortDuration.zero();
+        }
+        return result;
+    }
+
     @Override
     protected Object coerceFromString(String value) throws WrongValueException {
         EffortDuration result = EffortDuration.parseFromFormattedString(value);