Handle kingdom options more explicitly and consistently

[Aariq]

npn_species_state() and npn_species_type() both accept a kingdom argument. For both, it can be "Animalia", "Plantae" or NULL. If NULL it returns results for both. I think we should deprecate the NULL option and use

function(kingdom = c("Plantae", "Animalia", "both")) {
     kingdom <- rlang::arg_match(kingdom)
}

Also, the default for npn_species_state() is NULL and the default for npn_species_type() is "Plantae" and it might be good to make these consistent