Move signals for each country into their own files

[besentv]

Like the title says, the goal is to move signalling definitions for each country into their own files for easier navigation, and addition of future signalling systems.

Additionally, I added a license header to each file, like it's suggested by the project's license: https://github.com/OpenRailwayMap/OpenRailwayMap-CartoCSS/blob/master/COPYING#L623

[DerDakon]

This is a good move, but I don't like 2 things. First I would suggest to use short SPDX identifiers instead of copying the license text into each file. And given that you only moved lines around I don't see any reason that you should add your copyright into these files.

[besentv]

First I would suggest to use short SPDX identifiers instead of copying the license text into each file. And given that you only moved lines around I don't see any reason that you should add your copyright into these files.

Sure, I'll be changing it. :)

[besentv]

Done.

[Nakaner]

Some German and Austrian signals look identical and use the same styling rules. I would like to ask to move these signals to a file called signals_multiple_countries.mss (or a different name if you find a better one).

This applies for following signals:

• DE-ESO:ra10, AT-V2:verschubhalttafel
• DE-ESO:ra11, AT-V2:wartesignal
• DE-ESO:ne1, AT-V2:trapeztafel
• DE-ESO:so16, AT-V2:kreuztafel
• semaphore versions of DE-ESO:hp and AT-V2:hauptsignal

[besentv]

Some German and Austrian signals look identical and use the same styling rules. I would like to ask to move these signals to a file called signals_multiple_countries.mss (or a different name if you find a better one).

Did a general rebase and am going to apply this later.

[besentv]

I gave this some thoughts, but I'm not sure if I agree on adding a stylesheet for signals that share the same rules. The idea here is to have no code duplication, which makes perfectly sense, but adding a common file sort of defeats the purpose of splitting the code in the first place. Unfortunately, CartoCSS doesn't have a C or SASS style preprocessor. One proposal I could make is to have a makefile/python script that does that for us, or writing a custom version of the CartoCSS compiler.
So we'd end up having something like:

signals_common.mss:

@mixin shunting-stop() {
    marker-file: url('symbols/de/ra10.svg');
    marker-width: 16;
    marker-height: 11;
    marker-allow-overlap: true;
}

signals_at.mss:

[zoom>=17]["feature"="AT-V2:verschubsignal"]["shunting_form"="light"] {
    @include shunting-stop();
}

signals_de.mss:

[zoom>=17]["feature"="DE-ESO:ra10"]["shunting_form"="sign"] {
    @include shunting-stop();
}

[besentv]

@Nakaner Any thoughts on this?