Port EQMacEmu's Assist Aggro code

This code also allows you to toggle on Tick Pulling (Aggro:AllowTickPulling)
which was a pulling technique (exploit) fixed sometime in 2006

This code also implements assist caps to cut down on trains (5 by default)
Unsure if live what this number is (it exists) or if it's a per NPC basis

An NPC with Assist Aggro will not call for help, only NPCs with Primary Aggro will

zone/mob_ai.cpp

@@ -1735,8 +1735,10 @@ void Mob::AI_Event_Engaged(Mob* attacker, bool iYellForHelp) {
 	if (iYellForHelp) {
 		if(IsPet()) {
 			GetOwner()->AI_Event_Engaged(attacker, iYellForHelp);
-		} else {
+		} else if (!HasAssistAggro() && NPCAssistCap() < RuleI(Combat, NPCAssistCap)) {
 			entity_list.AIYellForHelp(this, attacker);
+			if (NPCAssistCap() > 0 && !assist_cap_timer.Enabled())
+				assist_cap_timer.Start(RuleI(Combat, NPCAssistCapTimer));
 		}
 	}
 
@@ -1787,6 +1789,8 @@ void Mob::AI_Event_NoLongerEngaged() {
 
 	if(IsNPC())
 	{
+		SetPrimaryAggro(false);
+		SetAssistAggro(false);
 		if(CastToNPC()->GetCombatEvent() && GetHP() > 0)
 		{
 			if(entity_list.GetNPCByID(this->GetID()))