Issue #89: Changed function OrderCheck to use json request/response

MtApi5/Requests/OrderCheckRequest.cs

@@ -0,0 +1,10 @@
+namespace MtApi5.Requests
+{
+    internal class OrderCheckRequest: RequestBase
+    {
+        public override RequestType RequestType => RequestType.OrderCheck;
+
+        public MqlTradeRequest TradeRequest { get; set; }
+
+    }
+}

MtApi5/Requests/OrderCheckResult.cs

@@ -0,0 +1,8 @@
+namespace MtApi5.Requests
+{
+    public class OrderCheckResult
+    {
+        public bool RetVal { get; set; }
+        public MqlTradeCheckResult TradeCheckResult { get; set; }
+    }
+}

MtApi5/Requests/RequestType.cs

@@ -8,6 +8,7 @@ namespace MtApi5.Requests
         CopyTicks       = 1,
         iCustom         = 2,
         OrderSend       = 3,
-        PositionOpen    = 4
+        PositionOpen    = 4,
+        OrderCheck      = 5
     }
 }