Add ability to visualize train signals

[Happyrobot33]

it would be nice if there was a way to turn on train signal rendering like exists on the ingame map. I use a lot of train signal displays in my world and these are just unreadable on the web map due to the way they function

[L0laapk3]

Are you talking about train block sections?

[Happyrobot33]

kind of, I use these kind of displays a lot where they use the train signals as the pixels

[L0laapk3]

Does this not already render with altmode? (Which is on by default, see --no-altmode)

[Happyrobot33]

no, since these dont actually have a alt mode in the base game. they only show up like this on the map

[Happyrobot33]

if you want more of an example of what I'm talking about, got to my hosted map

[L0laapk3]

I see. Factoriomaps has been on maintenance mode for quite a while for me, so its unlikely that I'll add this. However if you want to give it a go yourself, I'm more than happy to advise on how to add this and review/accept pull requests.