upgrade iso_generate_summary_table

[sebkopf]

• allow simplified use that takes all columns by default (if no ...) specified expect grouping columns, to generate the data table
• allow exclusion of data that is outside a 1, 2, 3 sigma range (see nu_tests in isoreader) - maybe will have to include an col_x n for each column to indicate how many of the total n were used for the calcluation (if no cutoff provided, can leave out these columns). note that this may be useful in a separate function that identifies_outliers first

[sebkopf]

duplicate of #14