Add option to force horizonal steps header in form wizard

[ziming]

Description

Currently on mobile devices, form wizard steps header is almost always vertically stacked even if I hide the all step header labels with ->hiddenLabel(). This makes the form wizard look unpleasant as can be seen below

What my PR does is you can now do this:

Wizard::make($steps)
    ->forceHorizontalStepsHeader();

And the horizontal steps header will be forced. Looking like this

The horizontal scroll bar if not all can fit into the screen

Hence making it better for those of us who didn't like the vertically stacked steps header look and want to force horizontal at all times even on mobile

[danharrin]

Hi, I would suggest using CSS to add these classes to .fi-fo-wizard-header. Then we do not need to introduce a new PHP method for a styling preference. Many thanks.