Add some dark halo for white trail names

[zstadler]

For example, the white trail near https://mapeak.com/poi/OSM/way_234989704

[HarelM]

It's worth mentioning that the trail color does not scale similar to the trail itself - the trail width increases while the trail color doesn't. I don't know if this is intentional or not.
The below screenshot is from the same place above when zooming in to maximum.