Apply the extra width mode on large displays across all pages, not just docs.

Fixes bug #66129 (Documentation does not follow the same layout pattern as
other pages).
Update the last modified CSS code to handle non-root working directories.
Shamelessly steal bjori's code to handle JS caching as well.
Add a router file for the built-in webserver

Usage: php -S localhost:8080 .router.php
Fit 3x mirrors per row on big screens