trip onadd in additional places

by request,
adds a per object-instance onadd for datablocks if an object instance *also* defines a class.
be mindful not to mix up which namespace is in use there, as you can not tag two different core class instances the same scripted class
implements the same with the same restrictions for simobjects in general

Engine/source/T3D/gameBase/gameBase.h

@@ -469,6 +469,8 @@ private:
    void _onDatablockModified();
 protected:
    void    onScopeIdChange() override { setMaskBits(ScopeIdMask); }
+
+   DECLARE_CALLBACK(void, onAdd, (SimObjectId ID));
 };