add DocSignedNotificationStatusHandler and implement the natification into EnveloepControler

EnvelopeGenerator.Domain/Constants/Format.cs

@@ -14,6 +14,12 @@ namespace EnvelopeGenerator.Domain.Constants
                 Formatting = Formatting.Indented,
                 NullValueHandling = NullValueHandling.Include
             };
+            public static readonly JsonSerializerSettings ForAnnotations = new JsonSerializerSettings()
+            {
+                ContractResolver = new CamelCasePropertyNamesContractResolver(),
+                Formatting = Formatting.None,                
+                NullValueHandling = NullValueHandling.Ignore
+            };
         }
         #endregion
     }