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.

lib/NetPacksBase.h

@@ -20,7 +20,6 @@ class CArmedInstance;
 class CArtifactSet;
 class CBonusSystemNode;
 struct ArtSlotInfo;
-class BattleInfo;
 
 #include "ConstTransitivePtr.h"
 #include "GameConstants.h"
@@ -28,7 +27,9 @@ class BattleInfo;
 
 struct DLL_LINKAGE CPack
 {
-	CPack() {};
+	std::shared_ptr<CConnection> c; // Pointer to connection that pack received from
+
+	CPack() : c(nullptr) {};
 	virtual ~CPack() {};
 
 	template <typename Handler> void serialize(Handler &h, const int version)
@@ -54,12 +55,11 @@ struct CPackForClient : public CPack
 
 struct CPackForServer : public CPack
 {
-	PlayerColor player;
-	CConnection *c;
+	mutable PlayerColor player;
+	mutable si32 requestID;
 	CGameState* GS(CGameHandler *gh);
 	CPackForServer():
-		player(PlayerColor::NEUTRAL),
-		c(nullptr)
+		player(PlayerColor::NEUTRAL)
 	{
 	}
 
@@ -69,6 +69,12 @@ struct CPackForServer : public CPack
 		return false;
 	}
 
+	template <typename Handler> void serialize(Handler &h, const int version)
+	{
+		h & player;
+		h & requestID;
+	}
+
 protected:
 	void throwNotAllowedAction();
 	void throwOnWrongOwner(CGameHandler * gh, ObjectInstanceID id);