make PyConf.reading functions usable as RecoConf.reco_objects_from_spruce

Unpacking of reco objects are duplicated in RecoConf.reco_objects_for_spruce and PyConf.reading. Make PyConf.reading functions usable as RecoConf.reco_objects_from_spruce so latter can be removed.

Needed for Moore!3203 (merged) DaVinci!1059 (closed)

Closing Moore#625 DaVinci#172