Reduce number of recursively included headers

This should improve compilation speed.

Things changed:
* Prefer forward-declarations in headers.
* Move header-includes out of headers if possible.
* Move some functions definitions out of headers.
* Put some member variables into unique_ptrs (see Client).

src/server/luaentity_sao.cpp

@@ -21,6 +21,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "luaentity_sao.h"
 #include "collision.h"
 #include "constants.h"
+#include "inventory.h"
 #include "player_sao.h"
 #include "scripting_server.h"
 #include "server.h"
@@ -409,7 +410,7 @@ void LuaEntitySAO::setHP(s32 hp, const PlayerHPChangeReason &reason)
 			m_env->getScriptIface()->luaentity_on_death(m_id, killer);
 		}
 		markForRemoval();
-	}	
+	}
 }
 
 u16 LuaEntitySAO::getHP() const

src/server/player_sao.h

@@ -21,6 +21,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #pragma once
 
 #include "constants.h"
+#include "metadata.h"
 #include "network/networkprotocol.h"
 #include "unit_sao.h"
 #include "util/numeric.h"

src/server/serveractiveobject.cpp

@@ -20,6 +20,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "serveractiveobject.h"
 #include <fstream>
 #include "inventory.h"
+#include "inventorymanager.h"
 #include "constants.h" // BS
 #include "log.h"
 
@@ -89,3 +90,8 @@ void ServerActiveObject::markForDeactivation()
 		m_pending_deactivation = true;
 	}
 }
+
+InventoryLocation ServerActiveObject::getInventoryLocation() const
+{
+	return InventoryLocation();
+}

src/server/serveractiveobject.h

@@ -19,10 +19,10 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #pragma once
 
+#include <cassert>
 #include <unordered_set>
 #include "irrlichttypes_bloated.h"
 #include "activeobject.h"
-#include "inventorymanager.h"
 #include "itemgroup.h"
 #include "util/container.h"
 
@@ -47,6 +47,8 @@ struct ItemStack;
 struct ToolCapabilities;
 struct ObjectProperties;
 struct PlayerHPChangeReason;
+class Inventory;
+struct InventoryLocation;
 
 class ServerActiveObject : public ActiveObject
 {
@@ -184,8 +186,7 @@ public:
 	// Inventory and wielded item
 	virtual Inventory *getInventory() const
 	{ return NULL; }
-	virtual InventoryLocation getInventoryLocation() const
-	{ return InventoryLocation(); }
+	virtual InventoryLocation getInventoryLocation() const;
 	virtual void setInventoryModified()
 	{}
 	virtual std::string getWieldList() const

src/server/serverinventorymgr.h

@@ -20,8 +20,11 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #pragma once
 
 #include "inventorymanager.h"
+#include <cassert>
 #include <functional>
+#include <unordered_map>
 
+class IItemDefManager;
 class ServerEnvironment;
 
 class ServerInventoryManager : public InventoryManager

src/server/unit_sao.cpp

@@ -21,6 +21,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "unit_sao.h"
 #include "scripting_server.h"
 #include "serverenvironment.h"
+#include "util/serialize.h"
 
 UnitSAO::UnitSAO(ServerEnvironment *env, v3f pos) : ServerActiveObject(env, pos)
 {