change charset to charpartition for genomes

[roblanf]

Right now when I run one of the alignments in IQ-TREE it loads all the charsets:

iqtree2 -s alignment.nex -p alignment.nex --redo

Loading 5 partitions...
Subset  Type    Seqs    Sites   Infor   Invar   Model   Name
1               145     531     54      425     1       COI_1stpos
2               145     531     3       502     2       COI_2ndpos
3               145     530     303     109     3       COI_3rdpos
4               145     1445    283     924     4       16S
5               145     3037    643     1960    1       mitochondrial_genome
Degree of missing data: 0.000
Info: multi-threading strategy over partitions

So instead of this:

begin SETS;

    [loci]
    CHARSET COI_1stpos = 1-1592\3;
    CHARSET COI_2ndpos = 2-1592\3;
    CHARSET COI_3rdpos = 3-1592\3;
    CHARSET 16S = 1593-3037;

    CHARPARTITION loci = 1:COI_1stpos, 2:COI_2ndpos, 3:COI_3rdpos, 4:16S;

    [genomes]
    CHARSET mitochondrial_genome = 1-3037;

    CHARPARTITION genomes = 1:mitochondrial_genome;

end;

we should have this:

begin SETS;

    [loci]
    CHARSET COI_1stpos = 1-1592\3;
    CHARSET COI_2ndpos = 2-1592\3;
    CHARSET COI_3rdpos = 3-1592\3;
    CHARSET 16S = 1593-3037;

    CHARPARTITION loci = 1:COI_1stpos, 2:COI_2ndpos, 3:COI_3rdpos, 4:16S;

    [genomes]
    CHARPARTITION   mitochondrial_genome = 1-3037;

    CHARPARTITION genomes = 1:mitochondrial_genome;

end;