Add a NMSSM input parameters class to help validating the user input.

This class will store *all* NMSSM input parameters (taken from the
SLHA file) and adds some helper functions to determine if the input
yields a Z3 symmetric model or not.
The NMSSM is Z3 symmetric even if xi_S != 0.

This is because the Z3 symmetry is a symmetry of the Superpotential,
and xi_S is a soft parameter.
Warn if more that 12 NMSSM parameters were set
set more NMSSM parameters to some debugging value
Put the NMSSM input parameters class into the header file and add
an operator<< for convenience.