Grid > Align center a box when there is only one box in a row

The grid is mostly used in Nuxeo on Summary views. Several rows and colums, with boxes in it.

When you need a simple box in a page, you should be able to select the width you want (gridStyle5, 6, etc) and this single box should be centered. (responsivene behavior)
A box with a full width (gridStyle12) won't be impacted by this change.

See screenshot:
*current_behavior: current state, not responsive

• grid_several_column: usual display of a grid, with many columns
• responsive_single_column1 & 2: behavior we have when resolving the task.