Issue #37: Used ConcurrencyMode.Multiple for server and client side to avoid deadlocks and freezes of MtApiService

MTApiService/ITaskExecutor.cs

@@ -0,0 +1,9 @@
+namespace MTApiService
+{
+    internal interface ITaskExecutor
+    {
+        void Execute(MtCommandTask task);
+        
+        int Handle { get; }
+    }
+}