Extend Pythia initialization tables to high energy

The .cmnd file in corsika-data/Pythia is the default one from the Pythia release. It only extends up to 1 PeV lab 10^6 GeV center-of-mass, which covers all collisions in the lab frame up to 10^{20} eV. It can be recalculated using code shipped with Pythia (main424.cc) if we were to extend our collision energy up to 10^{21} eV.

• Write test at high energy (10/100 EeV)
• Tested within Pythia 8.313 internally for collisions at 10^{20} and 10^{21} eV.

A new "official" file will be produced with the Pythia 8.315 8.316(?) going up to 10^7 GeV center-of-mass, therefore including collisions at 10^{21} eV aswell.

• Add updated pythia8315.cmnd to corsika-data/Pythia (corsika-data@c394042a)
• Link C8 to "pythia831x.cmnd" to corsika-data/Pythia from official release when available