Use "sim" or "obs" value for reference_var argument

[sbuis]

By default when type= "scatter" and select_scat= "res", residuals of each variables are plotted against their observed values.

reference_var can be used to plot residuals of each variables against a specific variable (observed or simulated values), but not against their simulated values.

We can thus plot residuals of each variables against their simulated values only by calling the plot function for each variable using the var argument.

Would be great if we could specify reference_var ="sim" and thus plot residuals of each variables against their simulated values using only one call to plot.