[BarPlot] - Setting sensible default bar widths for nonBandsMode

Closes #1156 
For @danmane , I will need to test this, but I believe the behavior should? work for nonlinear scales.  The reason I think so is that _getMinimumDataWidth is the width of what the bar should be in data space which means that regardless of being in a linear scale or log scale, this value should be the same in both.

Thus, when scaling the value, it will use whatever scale is backing the bar position to determine location/width.

Hope that makes sense.