Stepper should allow to circumvent the forced vertical direction on small devices

[NickGaens]

Is your feature request related to a problem? Please describe. A Stepper with a horizontal direction will force itself to switch to the vertical direction when viewed on a 'small' device, e.g. a portrait iPad.

Describe the solution you'd like I would like to optionally prevent the described behavior from happening. My suggestion would be to rename the forceVertical flag of Stepper to something like forceVerticalDirectionForSmall (defaulting to true) and exposing it via a setter. The MediaQuery listeners (on lines 147 and 152) should be revised accordingly then, though.