WIP on "book payment" Behat feature

Everything was going well, birds were singing and sun was shining... until my Mink session do strictly nothing when I submit the Stripe form :-/
"book payment" Behat feature now passes :-)

Didn't know that Mink did not authorize actions on hidden elements.. Even if it seems appropriate for a functional testing framework :-)
So... When the app env is "test", Stripe payment form now has visible inputs.