Core/Battlegrounds: Rework queues

* No more copies of Battleground classes
* FreesSlotQueues now have as key the MapId instead of queue id
* Random queues can now popup already busy specific battelgrounds (queues are NOT merged)
* Removed Holiday handling, this should already be handled in BattlegroundMgr::IsBGWeekend
Port From (https://github.com/TrinityCore/TrinityCore/commit/0ede6c155605da602b3bafaa3a1212d9f924759b)

Source/Game/Arenas/Arena.cs

@@ -29,10 +29,10 @@ namespace Game.Arenas
             StartMessageIds[BattlegroundConst.EventIdFourth] = ArenaBroadcastTexts.HasBegun;
         }
 
-        public override void AddPlayer(Player player)
+        public override void AddPlayer(Player player, BattlegroundQueueTypeId queueId)
         {
             bool isInBattleground = IsPlayerInBattleground(player.GetGUID());
-            base.AddPlayer(player);
+            base.AddPlayer(player, queueId);
             if (!isInBattleground)
                 PlayerScores[player.GetGUID()] = new ArenaScore(player.GetGUID(), player.GetBGTeam());