MAJOR: (*) Introduced LArSoft's MCParticle and MCTrajectory equivalent classes (mcpart & mctrack) and modified mctruth to mimic LArSoft's MCTruth (previously our mctruth was a combined object of all MC info in LArSoft). (*) Introduced a simple & dumb association storage mechanism in data_base: any data member can store associated data products' index number now. --kazu