WIP: Factory store config

After a closer look on how to store the initial configuration, I think it is only possible to store the configuration of the whole pdf and not it's sub-parts, as with diving into the recursion, RooObjects are added to the "config" (-> to the shared variables).

So the idea is to deepcopy the dict on the first level of recursion (where the config is only 'text-based') and, after creation of the whole factory, store it in the instance.

Next step is to manipulate and dump this config. Manipulation (like apply_fit_result to the config?) seems to belong to the (Base)Factory (or something different? MixIn?). Dumping as well?

What do you think @apuignav, where should we best place the manipulation/dump logic?