[7393] Implement access to client side holiday ids. Author: VladimirMangos

* src/game/GameEvent.* renamed to src/game/GameEventMgr.* for consistence
    * `game_event` now have new `holiday` field for store client side holiday id associated with game event
    * Added new enum HolidayIds with existed at this moment holiday ids.
    * New function "bool IsHolidayActive(HolidayIds id)" added accessabel from scripts for active holidays check.

--HG--
branch : trunk

src/game/Creature.cpp

@@ -46,7 +46,7 @@
 #include "GridNotifiersImpl.h"
 #include "CellImpl.h"
 #include "OutdoorPvPMgr.h"
-#include "GameEvent.h"
+#include "GameEventMgr.h"
 #include "PossessedAI.h"
 #include "CreatureGroups.h"
 // apply implementation of the singletons