don't render stations under constructions

With the exceptions for railway=station; this one has already a
"stillgelegt" icon.

Marked "sections" in layer-amenity-stations file.
imported sbahn/ubahn images from bbbike-aux/images
prepared rendering of disabled/under construction stations

But not enabled --- there's a rendering problem at Hauptbahnhof where
the in-construction S icon is over the U icon, but it should be
beneath.
rendering of disabled/under construction railways
rendering of disabled/under construction railways with tunnel=yes