Missing deep-copy getters for base object effectors

[Rick Stovall]

In cpp/sim_engine/base_object/base_object.h there are two protected lists of effectors:

struct base_object
{
(....)
protected:
  effector_list pre_attribs;
  effector_list post_attribs;
};

For reporting purposes there needs to be public getters assigned which return deep copies of these lists. It's very important the list not contain direct references to the objects stored in the working lists.