[7269] Use enum type for battleground queue type ids, and related cleanups.
* renamed a variable to make the content of it more clear: type->arenaslot
* renamed BattleGroundQueueTypeId-variables to bgQueueTypeId
just to make it easier reading the code (cause there existed
3 different names for this..)
* renamed GetBattleGroundQueueId to GetBattleGroundQueueTypeId
again this is just for better understanding
* Renamed [GS]etQueueType and m_Queue_type
* Renamed to [GS]etQueueId and m_QueueId
Signed-off-by: VladimirMangos <vladimir@getmangos.com>