Be able to reorder buttons in button bars

[LaurentG]

Currently, customizing a button bar, it's only possible to remove a button (or all buttons), or add a new button as last button of each bar.

As a result, to insert a button in the middle of an existing bar, we have to remove all the buttons below the one we want to insert, add the new button, and reinsert buttons we just removed.

This is not a big issue (since I guess nobody updates its button bars very frequently), but it would be nevertheless great to be able to re-order an existing bar, eg on the model of what is feasible with dashboards controls.

[Juanjo]

+1