Make WaypointMgr to singleton.

Move global waypoint_map variable to WaypointMgr's private variable.

--HG--
branch : trunk

src/game/World.cpp

@@ -1562,7 +1562,7 @@ void World::SetInitialWorldSettings()
     objmgr.LoadTrainerSpell();                              // must be after load CreatureTemplate
 
     sLog.outString("Loading Waypoints...");
-    WaypointMgr.Load();
+    sWaypointMgr->Load();
 
     sLog.outString("Loading Creature Formations...");
     formation_mgr.LoadCreatureFormations();