Core/Battlegrounds: Implement power resets on arena-fight preparations (first 60 seconds before arena-fight kicks off) (Thanks to Kaelima)

Restores all player powers every 5 seconds untill arena starts (fixes possible exploit with entering arena battle with full rage or runic power)
(The 5 second timer is not 100% confirmed, as official pages only states that the power is reset after prep-time - needs feedback)
Closes issue 4805

--HG--
branch : trunk

src/server/game/Entities/Player/Player.h

@@ -1993,6 +1993,8 @@ class Player : public Unit, public GridObject<Player>
         void _ApplyAllStatBonuses();
         void _RemoveAllStatBonuses();
 
+        void ResetAllPowers();
+
         void _ApplyWeaponDependentAuraMods(Item *item, WeaponAttackType attackType, bool apply);
         void _ApplyWeaponDependentAuraCritMod(Item *item, WeaponAttackType attackType, AuraEffect const * aura, bool apply);
         void _ApplyWeaponDependentAuraDamageMod(Item *item, WeaponAttackType attackType, AuraEffect const * aura, bool apply);