Update scatter_plot_from_table() so that plots can be made against labels or against values of another column (plus identity line, rescaled)
Add select_column_from_tables() and modify select_column_from_mindboggle_tables().
Updated scatter_plot_from_table() to accept lists as well as table file.
Allow plot_histograms() to accept lists, too.
Update table column selection functions to output columns with column headers (for hist/scatter plotting labels).