plot_int: Plot the additive, interactive, and difference genome scan
In duytpm16/qtl2utils: Modification of QTL2 Plots

Utilizes plot_scan1() to plot three LOD curves (additive, interactive, and difference) for a genome scan.

1	plot_int(add_scan, int_scan, diff_scan, map, lodcolumn = 1, chr = NULL)

`add_scan`	Output of `scan1()` without interactive covariates.
`int_scan`	Output of `scan1()` with interactive covariates.
`diff_scan`	Scan1 matrix containing the difference in LOD scores between the int_scan and add_scan.
`map`	A list of vectors of marker positions, as produced by `insert_pseudomarkers()`.
`lodcolumn`	LOD score column to plot (a numeric index, or a character string for a column name). Only one value allowed.
`chr`	Selected chromosomes to plot; a vector of character strings.