Adding quicktest to verify that selectBar on clusteredBars work

clusteredBars inherit the function from the parent AbstractBarPlot, so this functionality is essentially gotten for free.  Thus, this is mainly for verification.  I can add a unit test if need be / this quicktest doesn't necessarily have to exist.  At the reviewers' discretion.
Can we add a visual effect so that it's clear the bar was selected? One possibility is to define a scoped style block or something.