options for colour in plotComparedLargeScaleCharacteristics() restrictive

Currently impossible to colour by anything other than "cdm_name, cohort_name, variable_level, and type" even though more options are available when running availablePlotColumns().

Also, when those variables don't have multiple options available to colour by then it will not generate a plot at all. It would be great to be able to plot a 1:1 comparison between two cohorts for the variables like you can on PhenotypeR.