make iso_mark_calibration_range work with x/y variable renames

[sebkopf]

if a y or x value is renamed during iso_plot_data, then iso_mark_calibration_range will no longer recognize the range constraint anymore and it needs to be possible to tell the function which variable is actually which

one way to potential remedy this in a more autmoted way is to have all transformations that are applied to x and y during iso_plot_data ALSO applied to the calibration ranges that are stored inside the data frame! this is probably easiest if first nesting the dataset based on all calib_params fields (from all calibrations) and then doing the modifications in each evaluation ranges (keeping the original var names and ranges and adding the additional ones based on rename / mutate statements)