[Visualization for tabs] Add a new tab for the relationship between quantitative and nominal variables

[leijie-wang]

Correlation tab shows the relationship between two quantitative variables, while it seems that there should also be some tab showing the relationship between one nominal variable and one quantitative variable.

For now, sometimes, we could find such plots in the enhance tab, but only when we have referenced a specific column and then one more variable is added to create the enhance tab. We may expect that, from the beginning, whenever the dataframe is shown, such a tab appears.