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/AI/ScriptedAI/ScriptedFollowerAI.h

@@ -46,7 +46,7 @@ class FollowerAI : public ScriptedAI
 
         void MoveInLineOfSight(Unit*) override;
 
-        void EnterEvadeMode() override;
+        void EnterEvadeMode(EvadeReason /*why*/ = EVADE_REASON_OTHER) override;
 
         void JustDied(Unit*) override;