New improvements to the Pedestrian Working Group Visualizer thanks to @nickrsan!

- Simplified definitions of bronze-level crossings.
- Added a visual identifier for crossings that lack any tier level (previously bronze was displayed.)

Visualizer: https://overpass-ultra.us/#query=url:https://raw.githubusercontent.com/GA-Kevin-Codes/PWG-Visualizer/refs/heads/main/pwg-guide.ultra&m=10.32/40.6823/-73.8914
PR: https://github.com/GA-Kevin-Codes/PWG-Visualizer/pull/2

@kevin Thanks Kevin and thanks for making it! I think it's going to spur a ton of work improving the details of already mapped crossings - at least it's working for me!

And thanks for the suggestions to improve the PR like reminding me to make sure the sub-bronze level crossing visualization would work on multiple map backgrounds.

In case anyone wants to carry this over, the JOSM mapcss version still needs updating ;)