Made Network.h's Start() and Update pure virtual and removed cpp.

Removed unnecessary code from NetworkDefinitions.h.
Renamed sizeOfPackage to sizeOfPacket in Packet.cpp.

include/Engine/Network/Client.h

@@ -5,6 +5,7 @@
 #include <ctime>
 
 #include <glm/common.hpp>
+#include <boost/asio.hpp>
 
 #include "Network/MessageType.h"
 #include "Network/NetworkDefinitions.h"
@@ -21,8 +22,8 @@ class Client : public Network
 public:
     Client();
     ~Client();
-    void Start(World* world, EventBroker* eventBroker);
-    void Update();
+    void Start(World* world, EventBroker* eventBroker) override;
+    void Update() override;
     void Close();
 private:
     // Assio UDP logic