Allow Battlegrounds and arenas to be disabled by DB.

wtlk arenas disabled by default.

- Player will continue to see all bgs using UI, but won't be able to join disabled bg's
- Gossip menu not shown for disabled Bgs/arenas
- Id 6 disabled = all arenas disabled.
- Only id 6 arena enabled = Gossip shown but unable to join any arena

--HG--
branch : trunk

src/game/BattleGroundMgr.h

@@ -251,11 +251,13 @@ class BattleGroundMgr
 
         static bool IsBGWeekend(BattleGroundTypeId bgTypeId);
         void DoCompleteAchievement(uint32 achievement, Player * player = NULL);
+        bool isAnyArenaEnabled() const { return m_EnabledArenas.size() != 0; }
     private:
         BattleMastersMap    mBattleMastersMap;
 
         /* Battlegrounds */
         BattleGroundSet m_BattleGrounds[MAX_BATTLEGROUND_TYPE_ID];
+        std::vector<BattleGroundTypeId> m_EnabledArenas;
         std::vector<uint64> m_QueueUpdateScheduler;
         std::set<uint32> m_ClientBattleGroundIds[MAX_BATTLEGROUND_TYPE_ID][MAX_BATTLEGROUND_BRACKETS]; //the instanceids just visible for the client
         uint32 m_NextRatingDiscardUpdate;