Updated SI constants and fix for JIRA ticket CLHEP-156

Units - 17 July 2020 - G.Cosmo

• Updated values in SystemOfUnits.h and PhysicalConstants.h for:
  • e_SI, electron charge
  • h_Planck, Planck constant
  • Avogadro, Avogadro constant
  • k_Boltzmann, Boltzmann constant

based on May 2019 redefinition of SI units. References:

• https://en.wikipedia.org/wiki/2019_redefinition_of_the_SI_base_units
• https://www.britannica.com/science/electron-charge.

Random - 14 July 2020 - K.Savvidis, G.Cosmo

• Use 32-bit internal seeds types coherently in MixMaxRng. Addressing CLHEP JIRA ticket #156.