Move plasmid gene locations to end of iModulon gene scatter

[avsastry]

Currently, iModulon gene scatterplots just use chromosomal positions, so a gene at location 1 on the main chromosome, and location 1 on the plasmid overlap. A fix would include (a) Including chromosome in the gene_table file, and (b) if the chromosome exists, put the plasmids at position (genome length + plasmid position), and adding a vertical dashed line between each plasmid.