[Discover Tab] Move the cross that removes columns to the left of the column name

[mastropi]

Goal: Allow the user to remove columns fast --i.e. removing columns from the leftmost thru the rightmost with no need to move the mouse --after each click on the cross-- in search of the cross that will allow them to remove the column coming next to the right.

This is particularly useful when the user changes the table they wish to visualize, as the displayed columns from the previously selected table (which might be many) are still shown (with empty values if they do not exist in the newly selected table).

The following picture shows an example of this situation when the user switched from visualizing the columns of the INCOME table to visualizing the columns of the TASKS table (whose columns are all different from the INCOME table, and therefore all the INCOME columns appear with no value).
The idea would be to change the interface so that the cross currently shown on the right of the column name appears on its left.