Add export from nsi service

Hcs.TestApp/ClientDemo/NsiDemo.cs

@@ -5,13 +5,13 @@ namespace Hcs.ClientDemo
 {
     public class NsiDemo
     {
-        public static void DemoExportNsiItem(HcsClient client)
+        public static void DemoExportNsiItem51(HcsClient client)
         {
             var result = client.Nsi.GetNsiItem(51).Result;
             Console.WriteLine($"Результат операции:\r\n");
             foreach (var obj in result)
             {
-                Console.WriteLine(obj?.ToString());
+                Console.WriteLine(obj.ToJSON());
             }
         }
     }