Core/Battleground: Some (minor) code optimizations

- All access to Battleground vars are done using funtions (Remove friendship from Battleground and BattlegroundMgr)
- Move specific 47 mins arena check to battleground code as its generic to all arenas
- Create PreUpdateImpl and PostUpdateImpl functions. Specific battlegrounds will implement those if needed (No more need of call Battleground::Update inside specific BGs)
- Modify Create function to use only one parameter
- Remove EventPlayerCapturedFlag from Battleground class, only one BG implements it and it's not used outside that BG.

src/server/game/Battlegrounds/Zones/BattlegroundBE.cpp

@@ -44,20 +44,6 @@ BattlegroundBE::~BattlegroundBE()
 
 }
 
-void BattlegroundBE::Update(uint32 diff)
-{
-    Battleground::Update(diff);
-
-    if (GetStatus() == STATUS_IN_PROGRESS)
-    {
-        if (GetStartTime() >= 47*MINUTE*IN_MILLISECONDS)    // after 47 minutes without one team losing, the arena closes with no winner and no rating change
-        {
-            UpdateArenaWorldState();
-            CheckArenaAfterTimerConditions();
-        }
-    }
-}
-
 void BattlegroundBE::StartingEventCloseDoors()
 {
     for (uint32 i = BG_BE_OBJECT_DOOR_1; i <= BG_BE_OBJECT_DOOR_4; ++i)
@@ -127,7 +113,7 @@ void BattlegroundBE::HandleAreaTrigger(Player *Source, uint32 Trigger)
 
     //uint32 SpellId = 0;
     //uint64 buff_guid = 0;
-    switch(Trigger)
+    switch (Trigger)
     {
         case 4538:                                          // buff trigger?
             //buff_guid = m_BgObjects[BG_BE_OBJECT_BUFF_1];