This is a proposal to fix #3956.

There is:

1. a problem of cache busting in ace.js left open by 95fd5ce;
2. 4177b3f moved the font-face declarations from src/static/css/pad.css to two
   imported files in a different directory, and this requires a rebase on clean-css.

Tested the following 4 combinations with Firefox 75 on linux:

• minify: true|false

• directly invoking http://localhost:9001/p/somepad and http://localhost/pad/foo/p/somepad using the following nginx configuration:

  server {
          listen       80;
          server_name  pad.example.com;
  
          access_log  /var/log/nginx/eplite.access.log;
          error_log   /var/log/nginx/eplite.error.log;
  
      location /pad/foo {
          rewrite                /pad/foo/(.*) /$1 break;
          rewrite                ^/pad/foo$ /pad/foo permanent;
          proxy_pass             http://localhost:9001/;
          proxy_pass_header Server;
          proxy_redirect         / /pad/foo;
          proxy_set_header       Host $host;
          proxy_buffering off;
      }
  
      location /pad/foo/socket.io {
          rewrite /pad/foo/socket.io/(.*) /socket.io/$1 break;
          proxy_pass http://localhost:9001/;
          proxy_redirect         / /pad/foo/;
          proxy_set_header Host $host;
          proxy_buffering off;
          proxy_set_header Host $host;  # pass the host header
          proxy_http_version 1.1;  # recommended with keepalive connections
          # WebSocket proxying - from http://nginx.org/en/docs/http/websocket.html
          proxy_set_header Upgrade $http_upgrade;
          proxy_set_header Connection $connection_upgrade;
      }
  }