Minor: Improve docstring on asset_by_name()
Refactor filestree() to be available to any page

* state.py: Refactor rwalk() as walkWithoutGit() using os.walk()
* models.py: Refactor tree_in() as treeFromFilesystem(dir)
* Remove extrajs block from fonts.html and move folding JS to main.js
* Add filestree('out') to yaml.html
* Rework nav() to show Tests/Files for Upstream/Results (orthogonal UX)