Gantt chart as subplot

@johannesmichael

I updated the notebook posted as answer to the first question above, and the new version is posted here https://chart-studio.plot.ly/~empet/15256 .

I realized that all issues have been created by figs.update_layout. Using instead, figs.layout.xaxis.update(....),
figs.layout.xaxis2.update(....), etc, you can get the right plot.