Show plot for contingency table

[mccalluc]

• Fix In notebook, show a histogram for the contingency table #763
• also clean up calls to plot_bars, using positional params if it's just a dataframe and a title.
• There will be a small conflict with Synth notebook only gets the necessary utils #761, which removes the plot utils from synthetic data. Assuming that is merged first, before this is merged, we'll add back the plot utils here. (There may not be a merge conflict, but I would expect tests to fail unless this is resolved.)