This function is used to compare the distribution of concentration in the
sample and predicted data set. It shows three boxplots. One for the sample,
one for the predictions on days with sample values, and one for all days
(whether or not they had sample values).
Data come from named list, which contains a Sample dataframe with the sample data,
a Daily dataframe with the daily flow data,
and an INFO dataframe with metadata.
Although there are a lot of optional arguments to this function, most are set to a logical default.