Core/Scripts: Split OnCreatureCreate() and OnGameObjectCreate() into two virtual functions each.

Note to scripters: be aware that you will need to hook into the Remove functions if you want to do stuff at GO/creature removal.
Closes issue 5011.

--HG--
branch : trunk

src/server/game/Entities/GameObject/GameObject.cpp

@@ -125,7 +125,7 @@ void GameObject::AddToWorld()
     if (!IsInWorld())
     {
         if (m_zoneScript)
-            m_zoneScript->OnGameObjectCreate(this, true);
+            m_zoneScript->OnGameObjectCreate(this);
 
         sObjectAccessor.AddObject(this);
         WorldObject::AddToWorld();
@@ -138,7 +138,7 @@ void GameObject::RemoveFromWorld()
     if (IsInWorld())
     {
         if (m_zoneScript)
-            m_zoneScript->OnGameObjectCreate(this, false);
+            m_zoneScript->OnGameObjectRemove(this);
 
         // Possible crash at access to deleted GO in Unit::m_gameobj
         if (uint64 owner_guid = GetOwnerGUID())