use icons from railway-signals instead of own icons, add " to stylesheet

- use German Ne2 and Ne5 from Nakaner's railway-signals
- use icon for German semaphore distant signal from Nakaner's
  railway-signals
- add quotations marks to stylesheet for JOSM compatability
add SVG source for changed semaphore distant signal icon
add German Zs10 from Nakaner's railway-signals/Wikimedia Commons