Clean up static_cast enum messes

[kc9jud]

Currently there are many places with code like

char radial_operator_type_c;
line_stream >> radial_operator_type_c;
shell::RadialOperatorType radial_operator_type = static_cast<shell::RadialOperatorType>(radial_operator_type_c);

or

std::string operator_species_s;
line_stream >> operator_species_s;
basis::OperatorTypePN operator_species = kCharCodeOperatorTypePN.at(operator_species_s);

There are also analogous lookups going the other direction, from enum->string/char. This is dangerous and not type-safe. This should be replaced with some templatized lookup functions, perhaps like https://github.com/andrewstephens75/EnumMapping

This probably belongs in https://github.com/nd-nuclear-theory/mcutils