Scripts/Instances: Complete rewrite of the boundary system.

- Migrate boundary logic to Maps/AreaBoundary instead of having it sit in InstanceScript (to possibly allow use for other purposes).
- Implement the first five boundary types in Maps/AreaBoundary.cpp.
- Add boundary checks to Creature's update logic
- Add boundary data for all Northrend raids
- Add boundary initialization structures and methods to InstanceScript
- Modify EnterEvadeMode signature. It now passes a value from the EvadeReason enum as parameter to allow special casing depending on evade reason
- Remove previous (weird) boundary code that had them linked to GO spawns

src/server/game/Entities/Unit/Unit.cpp

@@ -12683,7 +12683,7 @@ void Unit::TauntFadeOut(Unit* taunter)
     if (m_ThreatManager.isThreatListEmpty())
     {
         if (creature->IsAIEnabled)
-            creature->AI()->EnterEvadeMode();
+            creature->AI()->EnterEvadeMode(CreatureAI::EVADE_REASON_NO_HOSTILES);
         return;
     }
 
@@ -12824,7 +12824,7 @@ Unit* Creature::SelectVictim()
     }
 
     // enter in evade mode in other case
-    AI()->EnterEvadeMode();
+    AI()->EnterEvadeMode(CreatureAI::EVADE_REASON_NO_HOSTILES);
 
     return NULL;
 }