Generalise ParamSpace.get_info_dict

The following discussion from !57 (merged) should be addressed:

• @blsqr started a discussion:

  This part is potentially problematic: It's currently unclear to me, how to best communicate this information in an unambiguous and robust way, let alone extract that information without writing too much code on this level...

  Basically, the issue is that with masks, the parameter space iteration is changed and pdim.values will contain Masked objects. Should these then be simply removed from the information dict returned here? Or should they be represented additionally?

  This probably needs some more thought and experience. To avoid trouble, dumping that information with any masks applied is currently not supported; this problem should be solved separately.