add Nucleus to corsika id conversion

for nuclei we want to be able to use the nucleon number to define nuclei, i.e. Code nucleonNum2corsika( int A )

for hadronic interactions the distinction between isotopes is irrelevant but for tracking in the presence of magnetic fields it will matter. To convert pure nucleon number into a nucleus(A,Z) we would need a default list of stable nuclei. I believe this is how it is done in CORSIKA7.

required for #90 (closed) and #65 (closed)

related to #125 (closed)