Added UDP multicast for plugin discovery (#153)

* Added Timer

* Added UDPSocket::GetAddr

* Added MessageHandlers::SendBeacon()

* PoC of starting a timer on PluginEnable

* C++11

* Added Timer to xcode project

* C++11 in cmake

* added Timer to cmake

* use function pointer in Timer

* moved Timer to namespace

+ wait for thread to join when stopping the timer

* Windows: changed uint to unisgned short

* Windows: Added Timer.h/cpp to project

* GetAddr static

* Send xplane and plugin version with BECN

* SendBeacon with params

* fixed file copyrights

* Include functional

to fix Linux compile error

* review fixes

* Send plugin receive port in BECN

* review fixes

xpcPlugin/Timer.h

@@ -0,0 +1,29 @@
+// Copyright (c) 2013-2018 United States Government as represented by the Administrator of the
+// National Aeronautics and Space Administration. All Rights Reserved.
+
+#ifndef XPCPLUGIN_TIMER_H_
+#define XPCPLUGIN_TIMER_H_
+
+#include <stdio.h>
+#include <iostream>
+#include <thread>
+#include <chrono>
+#include <functional>
+
+namespace XPC {
+    class Timer
+    {        
+        std::atomic_flag running;
+        std::thread th;
+        
+    public:
+
+        using Callback = std::function<void(void)>;
+        
+        void start(const std::chrono::milliseconds, const Callback &callback);
+        
+        void stop();
+    };
+}
+
+#endif /* Timer_hpp */