Add another air traffic controller example for mediator

src/MediatorPattern/GroundAirTrafficControl/AirTrafficControl.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace MediatorPattern.GroundAirTrafficControl
+{
+    public class AirTrafficControl : IAirTrafficControlTower
+    {
+        List<Lane> lanes;
+        object lockLanes = new object();
+        public AirTrafficControl(List<Lane> lanes)
+        {
+            this.lanes = lanes;
+        }
+        public bool RequestLaneForMaintainance(MaintainerTeam team, Lane lane)
+        {
+            var requestedLane = lanes.FirstOrDefault(l => l.ID == lane.ID);
+
+            if (requestedLane == null)
+                return false;
+            lock (lockLanes)
+            {
+                if (requestedLane.IsAvailable)
+                {
+                    requestedLane.IsAvailable = false;
+                    Console.WriteLine("Lane {0} is now used by maintainers", lane.ID);
+                    return true;
+                }
+                else
+                {
+                    Console.WriteLine("Lane {0} cannot be used by maintainers because it's already in use", lane.ID);
+                    return false;
+                }
+            }
+        }
+
+        public Optional<Lane> RequestPermissionToLand(Plane plane)
+        {
+            lock (lockLanes)
+            {
+                var availableLane = lanes.FirstOrDefault(l => l.IsAvailable);
+
+                if (availableLane != null)
+                {
+                    availableLane.IsAvailable = false;
+                    Console.WriteLine("Approved landing for plane {0} on lane {1}", plane.ID, availableLane.ID);                    
+                    return Optional<Lane>.Of(availableLane);
+                }
+                else
+                {
+                    Console.WriteLine("Landing not approved for plane {0}", plane.ID);
+                    return Optional<Lane>.Empty;
+                }
+            }
+        }
+    }
+}