3.0: Visual hint for resizable columns

[mnscholz]

Almost all listings/tables have resizable columns. However, there is no permantent visual hint for this feature.
I found out that this is possible when incidentally hovering the mouse over the column header margin. In this case the cursor changes and the column header margin is highlighted.

This feature should be made visible somehow.

The tables of the Kitodo desktop don't seem to be resizable. It would be nice to have it there too, since cell space is less and contents get cropped on smaller viewports.