Add a color to show dual electrification areas

[JonathanBittner]

There are areas where there is dual electrification modes electrification=contact_line;rail or electrification=rail;contact_line. Presently these lines show up in "ambiguous gray." (@railway_fill_color: grey; ??) I think it would be difficult to try to render both the third rail voltage/frequency color and the overhead voltage/frequency color. I suggest creating an additional color that stands out and isn't on the red-to-violet spectrum used for the voltages perhaps a silvery gray that could stand out. Maybe something between #c0c0c0 and #dcdcdc.

The most prominent area I know is around the New York Penn Station complex including the Empire Connection tunnel, East River Tunnels, and Sunnyside Yard. There, Amtrak corridor trains with overhead electrification, LIRR trains with third rail electrification, and Amtrak Empire Service trains with third rail electrification share trackage. Things will become more interesting as it has been proposed to extend third rail up the Hell Gate line for Metro-North Penn Station Access. The tagging for that will be fun ('electrified'='contact_line' AND 'proposed:electrified'='rail', etc.) I wouldn't even try to render it.

This something I'd like to work on after bug #47 is fixed and pull request #57 has been merged.

[JonathanBittner]

Question: should we have a single color to designate lines with dual electrification or should we try to add a second layer to show the second color as a dashed line? I know the gauge style tries to do a second and even third layer.

[TrainTraveler]

When developing the gauge style, i faced the same question of whether to use a own color or a two or three colered dashed line. The gauge style has now been in use for a year and i am not aware of any displaying problems. As a user, i would prefer the dashed variant because the meaning is more intuitive and you can then also simpler recognize which two electrifications occur.