Function to create a legend for autosomal trisomy
.addLegendAutosomalTrisomy.bexy(x_coord, y_coord, scaffoldName, colors)
No return value, called for side effects.
The x-coordinate for legend.
The y-coordinate for legend.
The name of the scaffold to plot (has to be an autosome).
A vector of length two with the colors for triploid and diploid samples, respectively.