Route layer

[hiddewie]

Part of #413

Work in progress.

Preliminary Germany rendering with colors for the amount of routes on a line:

[entbert]

I really like the idea, but does this simply count the type=route relations? In that case, I don't think that this number is of much value. For example, the line to Norddeich sees one train every our, but is included in 8 relations as these trains run under different route numbers and to different destinations. Thus this line is displayed in orange while others with the same number of trains are coloured blue as all trains there have the same destination.

A more meaningful quantity would be the number of trains per hour on a given line which in theory could be determined from the interval tag, but that is often missing.

[entbert]

I also noticed on the map that the number of routes doubles where a lines changes from 2 to 1 tracks. From a passenger's point of view this seems unnatural as the service level doesn't get better. But I guess it makes sense when you look at it from the infrastructure side. (But then again, infrastructure-wise, the number of routes is less important than the number of trains -- even more so then for passengers.)