Allow ZIP files whose paths are relative to the ZIP root in JOSM's map styling

[skorasaurus]

HOT OSM is making a map styling for josm and would like to distribute it through a zip file since many of our users will be in areas
with limited and sporadic internet connections.

We're also currently using github to manage it and Github automatically generates zip files based on the tag, (i.e. : ​https://github.com/hotosm/HDM-JOSM-style/archive/0.0.1.zip

Unfortunately, these zip files aren't usable in josm for the map coloring because the icons path is relative to the zip root, not to the file itself. Using the default zip export from github could make the workflow much easier

If you could, we'd greatly appreciate it.