Full rework of pre-game interface and networking

New features for players:
* Loading for multiplayer. Any save could be used for multiplayer.
* Restart for multiplayer. All clients will restart together.
* Loading from single save.
* Hotseat mixed with network game. Multiple players per client.
* Now connection to server could be cancelled.
* Return to menu on disconnections instead of crashes.
* Restoring of last selected map, save or campaign on next run.

TLDR on important changes in engine code:
* UI: work with server separated from UI
* UI: all explitic blitting replaced with IntObject's
* UI: all new code use smart pointers instead of DISPOSE
* Gameplay always start through lobby controlled by server.
* Threads receiving netpacks now shared for lobby and gameplay.
* Campaigns: heroes for crossover now serialized as JsonNode.

client/NetPacksLobbyClient.cpp

@@ -0,0 +1,142 @@
+/*
+ * NetPacksLobbyClient.cpp, part of VCMI engine
+ *
+ * Authors: listed in file AUTHORS in main folder
+ *
+ * License: GNU General Public License v2.0 or later
+ * Full text of license available in license.txt file, in main folder
+ *
+ */
+#include "StdInc.h"
+
+#include "lobby/CSelectionBase.h"
+#include "lobby/CLobbyScreen.h"
+
+#include "lobby/OptionsTab.h"
+#include "lobby/RandomMapTab.h"
+#include "lobby/SelectionTab.h"
+#include "lobby/CBonusSelection.h"
+
+#include "CServerHandler.h"
+#include "CGameInfo.h"
+#include "gui/CGuiHandler.h"
+#include "widgets/Buttons.h"
+#include "widgets/TextControls.h"
+
+#include "../lib/CConfigHandler.h"
+#include "../lib/CGeneralTextHandler.h"
+#include "../lib/NetPacksLobby.h"
+#include "../lib/serializer/Connection.h"
+
+bool LobbyClientConnected::applyOnLobbyHandler(CServerHandler * handler)
+{
+	// Check if it's LobbyClientConnected for our client
+	if(uuid == handler->c->uuid)
+	{
+		handler->c->connectionID = clientId;
+		if(!settings["session"]["headless"].Bool())
+			GH.pushInt(new CLobbyScreen(static_cast<ESelectionScreen>(handler->screenType)));
+		handler->state = EClientState::LOBBY;
+		return true;
+	}
+	return false;
+}
+
+void LobbyClientConnected::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	if(uuid == handler->c->uuid)
+	{
+	}
+}
+
+bool LobbyClientDisconnected::applyOnLobbyHandler(CServerHandler * handler)
+{
+	if(clientId != c->connectionID)
+		return false;
+
+	handler->stopServerConnection();
+	return true;
+}
+
+void LobbyClientDisconnected::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	GH.popIntTotally(lobby);
+}
+
+void LobbyChatMessage::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	if(lobby)
+	{
+		lobby->card->chat->addNewMessage(playerName + ": " + message);
+		lobby->card->setChat(true);
+		if(lobby->buttonChat)
+			lobby->buttonChat->addTextOverlay(CGI->generaltexth->allTexts[531], FONT_SMALL);
+	}
+}
+
+void LobbyGuiAction::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	if(!handler->isGuest())
+		return;
+
+	switch(action)
+	{
+	case NO_TAB:
+		lobby->toggleTab(lobby->curTab);
+		break;
+	case OPEN_OPTIONS:
+		lobby->toggleTab(lobby->tabOpt);
+		break;
+	case OPEN_SCENARIO_LIST:
+		lobby->toggleTab(lobby->tabSel);
+		break;
+	case OPEN_RANDOM_MAP_OPTIONS:
+		lobby->toggleTab(lobby->tabRand);
+		break;
+	}
+}
+
+bool LobbyStartGame::applyOnLobbyHandler(CServerHandler * handler)
+{
+	if(handler->state == EClientState::GAMEPLAY)
+	{
+		handler->endGameplay(false);
+	}
+	handler->state = EClientState::STARTING;
+	if(handler->si->mode != StartInfo::LOAD_GAME)
+	{
+		handler->si = initializedStartInfo;
+	}
+	if(settings["session"]["headless"].Bool())
+		handler->startGameplay();
+	return true;
+}
+
+void LobbyStartGame::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	CMM->showLoadingScreen(std::bind(&CServerHandler::startGameplay, handler));
+}
+
+bool LobbyUpdateState::applyOnLobbyHandler(CServerHandler * handler)
+{
+	hostChanged = state.hostClientId != handler->hostClientId;
+	static_cast<LobbyState &>(*handler) = state;
+	return true;
+}
+
+void LobbyUpdateState::applyOnLobbyScreen(CLobbyScreen * lobby, CServerHandler * handler)
+{
+	if(!lobby->bonusSel && handler->si->campState && handler->state == EClientState::LOBBY_CAMPAIGN)
+	{
+		lobby->bonusSel = new CBonusSelection();
+		GH.pushInt(lobby->bonusSel);
+	}
+
+	if(lobby->bonusSel)
+		lobby->bonusSel->updateAfterStateChange();
+	else
+		lobby->updateAfterStateChange();
+
+	if(hostChanged)
+		lobby->toggleMode(handler->isHost());
+}