Drop content_sao.{cpp,h}

Move LuaEntitySAO to a new dedicated file
Drop TestSAO (useless object)
Drop the old static startup initialized SAO factory, which was pretty useless.
This factory was using a std::map for 2 elements, now just use a simple condition owned by ServerEnvironment, which will be lightweight, that will also drop a one time useful test on each LuaEntitySAO creation. This should reduce server load on massive SAO creation

src/script/lua_api/l_env.cpp

@@ -33,12 +33,12 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "nodedef.h"
 #include "daynightratio.h"
 #include "util/pointedthing.h"
-#include "content_sao.h"
 #include "mapgen/treegen.h"
 #include "emerge.h"
 #include "pathfinder.h"
 #include "face_position_cache.h"
 #include "remoteplayer.h"
+#include "server/luaentity_sao.h"
 #include "server/player_sao.h"
 #ifndef SERVER
 #include "client/client.h"

src/script/lua_api/l_item.cpp

@@ -25,7 +25,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "itemdef.h"
 #include "nodedef.h"
 #include "server.h"
-#include "content_sao.h"
 #include "inventory.h"
 #include "log.h"
 

src/script/lua_api/l_object.cpp

@@ -27,11 +27,11 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "common/c_content.h"
 #include "log.h"
 #include "tool.h"
-#include "content_sao.h"
 #include "remoteplayer.h"
 #include "server.h"
 #include "hud.h"
 #include "scripting_server.h"
+#include "server/luaentity_sao.h"
 #include "server/player_sao.h"
 
 /*