Hardening of the Frontend docker image (#377)

* move the env-config script to a sub folder
* fix doc
* fix ports and ref to the official image
* add hardening to the docker-compose examples

frontend/nginx/nginx.conf

@@ -1,4 +1,3 @@
-user  nginx;
 worker_processes  auto;
 worker_rlimit_nofile  30000;
 
@@ -19,13 +18,13 @@ http {
 
     access_log  /var/log/nginx/access.log  main;
     sendfile        on;
-    #tcp_nopush     on;
+
     keepalive_timeout  65;
     gzip  on;
     include /etc/nginx/conf.d/*.conf;
 
     server {
-        root /usr/share/nginx/html;
+        root /app;
         index index.html;
         listen 8000;
         listen [::]:8000;