Add base directory support

- Base directory can be changed in config.py from the default / to, for example, /taiko-web/
  - See tools/nginx_subdir.conf for an example nginx configuration with a base directory
- Custom error pages can be used, they can be set in config.py

tools/nginx_subdir.conf

@@ -0,0 +1,28 @@
+server {
+	listen 80;
+	#server_name taiko.example.com;
+	
+	location /taiko-web/ {
+		proxy_set_header X-Real-IP $remote_addr;
+		proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+		proxy_set_header Host $server_name;
+		proxy_pass http://127.0.0.1:34801;
+	}
+	
+	location ~ ^/taiko-web/(assets|songs|src)/ {
+		rewrite ^/taiko-web/(.*) /$1 break;
+		root /srv/taiko-web/public;
+		location ~ ^/taiko-web/songs/([0-9]+)/preview\.mp3$ {
+			set $id $1;
+			rewrite ^/taiko-web/(.*) /$1 break;
+			try_files $uri /taiko-web/api/preview?id=$id;
+		}
+	}
+	
+	location /taiko-web/p2 {
+		proxy_http_version 1.1;
+		proxy_set_header Upgrade $http_upgrade;
+		proxy_set_header Connection "Upgrade";
+		proxy_pass http://127.0.0.1:34802;
+	}
+}