R6 Bar chart contrasting dependencies for different software version

[cbogart]

Visualizaiton/chart contrasting used-with patterns of different versions (i.e. Package Xv1 was used with ggplot but PackageXv2 was used with ggvis, and this distinction can/cannot be explained by a general shift over time from Xv1 to Xv2 and ggplot to ggvis).