Column sorting buttons in matrix visual with column hierarchy

[eflory-stio]

Enable column sorting buttons for measures in matrix visuals even when the measures are grouped by a field in the columns section. Currently, these column sorting buttons (displayed when cursor hovers over column header) are only present when matrix visuals do not contain any fields in the "Columns" section. Having these column sorting buttons always available would greatly improve the intuitiveness of sorting matrix visuals.