Added and tested the network queue in the server

This is a reimplementation of the old network queue, but using a class.
This still uses a separate thread, so that packets can wait if there's any
lag. Really, thinking about it, I wonder how necessary this was.

On the upside, no singletons this time. Which means that you can have
several instances of UDPNetworkManager. That's unintentional, but good to
know.

server/server_application.hpp

@@ -23,6 +23,7 @@
 #define SERVERAPPLICATION_HPP_
 
 #include "udp_network_utility.hpp"
+#include "network_queue.hpp"
 
 #include "sqlite3/sqlite3.h"
 #include "SDL/SDL.h"
@@ -52,6 +53,7 @@ private:
 	sqlite3* database = nullptr;
 
 	UDPNetworkUtility networkUtil;
+	NetworkQueue networkQueue;
 	std::list<ClientEntry> clientEntries;
 };