Server class code cleanups (#9769)

* Server::overrideDayNightRatio doesn't require to return bool
There is no sense to sending null player, the caller should send a valid object

* Server::init: make private & cleanup
This function is always called before start() and loads some variables which can be loaded in constructor directly.
Make it private and call it directly in start

* Split Server inventory responsibility to a dedicated object

This splits permit to found various historical issues:
* duplicate lookups on player connection
* sending inventory to non related player when a player connects
* non friendly lookups on detached inventories ownership

This reduce the detached inventory complexity and also increased the
lookup performance in a quite interesting way for servers with thousands
of inventories.

src/script/lua_api/l_base.h

@@ -38,12 +38,14 @@ class GUIEngine;
 class ScriptApiBase;
 class Server;
 class Environment;
+class ServerInventoryManager;
 
 class ModApiBase : protected LuaHelper {
 
 public:
 	static ScriptApiBase*   getScriptApiBase(lua_State *L);
 	static Server*          getServer(lua_State *L);
+	static ServerInventoryManager *getServerInventoryMgr(lua_State *L);
 	#ifndef SERVER
 	static Client*          getClient(lua_State *L);
 	static GUIEngine*       getGuiEngine(lua_State *L);