Update nginx.conf

Increase buffer to avoid 502 with some plugins (spxplugindownloader, ...)
According to https://wiki.pluxml.org/installer/nginx/ : 
* increase security
* setup cache control
* setup redirect

conf/nginx.conf

@@ -1,4 +1,9 @@
 #sub_path_only rewrite ^__PATH__$ __PATH__/ permanent;
+
+location @handler {
+  rewrite ^/(.*)$ /index.php?^$1 last;
+}
+
 location __PATH__/ {
 
   # Path to source
@@ -9,24 +14,56 @@ location __PATH__/ {
     rewrite ^ https://$server_name$request_uri? permanent;
   }
 
-### Example PHP configuration (remove it if not used)
   index index.php;
-
+  
-  # Common parameter to increase upload size limit in conjunction with dedicated php-fpm file
+  # Réécriture vers l'index
-  #client_max_body_size 50M;
-
   try_files $uri $uri/ index.php;
+
+  # Parseur PHP
   location ~ [^/]\.php(/|$) {
     fastcgi_split_path_info ^(.+?\.php)(/.*)$;
     fastcgi_pass unix:/var/run/php/php7.0-fpm-__NAME__.sock;
-
     fastcgi_index index.php;
     include fastcgi_params;
     fastcgi_param REMOTE_USER $remote_user;
     fastcgi_param PATH_INFO $fastcgi_path_info;
     fastcgi_param SCRIPT_FILENAME $request_filename;
+    fastcgi_buffers 16 16k;
+    fastcgi_buffer_size 32k;
+  }
+
+  # Redirections
+  ## Flux RSS
+  location /feed/ {
+    rewrite ^/feed\/(.*)$ /feed.php?^$1 last;
+  }
+  ## Sitemap
+  location = /sitemap.xml {
+    rewrite .* /sitemap.php;
+  }
+
+  # Protections
+  location ~ /(version|update|readme|data/configuration) {
+    deny all;
+  }
+
+  # Cache-control
+  location /data/ {
+    add_header Cache-Control public;
+    expires 12h;
+  }
+  location /core/ {
+    add_header Cache-Control public;
+    expires 12h;
+  }
+  location /plugins/ {
+    add_header Cache-Control public;
+    expires 12h;
+  }
+  location /themes/ {
+    add_header Cache-Control public;
+    expires 12h;
   }
-### End of PHP configuration part
 
   # Include SSOWAT user panel.
   include conf.d/yunohost_panel.conf.inc;