send the billing code along with the query

Yavsc.Abstract/Billing/BillingCodes.cs

@@ -0,0 +1,10 @@
+namespace Yavsc.Models.Billing
+{
+    public static class BillingCodes
+    {
+        public const string Rdv = "Rdv";
+        public const string MBrush = "MBrush";
+
+        public const string Brush = "Brush";
+    }
+}

Yavsc.Abstract/Billing/IBillable.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 namespace Yavsc.Billing
 {
     public interface IBillable {
+        string BillingCode { get; set; }
         string GetDescription ();
         List<IBillItem> GetBillItems();
         long Id { get; set; }