GrampsWeb's fonts.css references fonts as url('fonts/MaterialIcons.woff2').
Since fonts.css is served from /ahnenforschung/fonts/fonts.css, the browser
resolves this to /ahnenforschung/fonts/fonts/MaterialIcons.woff2 (double
fonts/ directory). Strip the fonts/ prefix via sub_filter so the URL
resolves correctly to /ahnenforschung/fonts/MaterialIcons.woff2.
Co-Authored-By: Paperclip <noreply@paperclip.ing>