Enables styling the Orbit extension via the orbit scss-variables as documented in the Foundation Orbit manuals

Fix to make the following foundation scss-variables work for the Orbit extension:

    $orbit-bullet-nav-color 
    $orbit-bullet-nav-color-active
    $orbit-slide-number-bg (and set default to use rgb-alpha)
    $orbit-slide-number-font-color
    $orbit-slide-number-padding