Network Layer 7 rework (Packet handling)

* Move networkcode to a dedicated directory
* Rename clientserver.h to network/networkprotocol.h (Better name) and sanitize some includes
* Create object NetworkPacket
  * It stores command (opcode) and data separated
  * It also stores peer_id
  * Data reading can be done by using a streaming interface
* Change packet routing analysis
  * Remove old conditional analysis
  * Now uses function pointed analysis and add connection state ({Client,Server}::handlers)
  * Connection state permit to categorize condition to handle before analyze packets
  * Create a handler for depreciated messages, instead of duplicating code

src/guiFormSpecMenu.h

@@ -28,7 +28,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "inventorymanager.h"
 #include "modalMenu.h"
 #include "guiTable.h"
-#include "clientserver.h"
+#include "network/networkprotocol.h"
 
 class IGameDef;
 class InventoryManager;