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/server/CMakeLists.txt

@@ -4,5 +4,6 @@ set(server_SRCS
 	${CMAKE_CURRENT_SOURCE_DIR}/mods.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/player_sao.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/serveractiveobject.cpp
+	${CMAKE_CURRENT_SOURCE_DIR}/serverinventorymgr.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/unit_sao.cpp
 	PARENT_SCOPE)