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/Framework/Constants/SharedConst.cs

@@ -113,7 +113,7 @@ namespace Framework.Constants
         /// </summary>
         public const int PvpTeamsCount = 2;
         public const uint CountOfPlayersToAverageWaitTime = 10;
-        public const uint MaxPlayerBGQueues = 2;
+        public const uint MaxPlayerBGQueues = 3;
         public const uint BGAwardArenaPointsMinLevel = 71;
         public const int ArenaTimeLimitPointsLoss = -16;
         public const int MaxArenaSlot = 3;