Added ModifiedOrdersMonitor, added some more doc

MtApi/Monitors/OrderModification/ModifiedOrdersEventArgs.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace MtApi.Monitors
+{
+    public class ModifiedOrdersEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Returns a list of all modified orders
+        /// </summary>
+        public List<MtModifiedOrder> ModifiedOrders { get; }
+        public ModifiedOrdersEventArgs(List<MtModifiedOrder> modifiedOrders)
+        {
+            ModifiedOrders = modifiedOrders;
+        }
+    }
+}