Core/Creature: Add facilities to the Creature class to allow setting an automated, periodic pulse that puts every player in the zone in combat and on the creature's threat list.

Scripts/BossAI: Set the BossAI parent class to make use of this in its _EnterCombat and _Reset methods. Combat pulses happen every 5 seconds.

(cherry picked from commit d57193df444b719757ae1da4a5f19e204074f6ae)

# Conflicts:
#	src/server/game/AI/ScriptedAI/ScriptedCreature.cpp
#	src/server/game/Entities/Creature/Creature.cpp

src/server/game/AI/ScriptedAI/ScriptedCreature.cpp

@@ -453,6 +453,7 @@ void BossAI::_Reset()
     if (!me->IsAlive())
         return;
 
+    me->SetCombatPulseDelay(0);
     me->ResetLootMode();
     events.Reset();
     summons.DespawnAll();
@@ -470,6 +471,7 @@ void BossAI::_JustDied()
 
 void BossAI::_EnterCombat()
 {
+    me->SetCombatPulseDelay(5);
     me->setActive(true);
     DoZoneInCombat();
     if (instance)