Enable nginx by default, and override the favicon to find the right tab easier

Enable nginx by default since we use it in production and it has broken things before ( https://gitlab.com/gitlab-org/gitlab-ce/issues/27054#note_21914305 )

Was also necessary (easier) to have a GDK-specific favicon for #186

Closes #186

Question: if we should use nginx infront of rails, should rails talk purely over unix-socket? Nginx currently binds on :3443 :3080 (TLS was removed)

nginx/conf/nginx.conf.example

@@ -41,7 +41,7 @@ http {
   server {
     listen 127.0.0.1:3080;
-    location ~* favicon.*\.ico$ {
+    location ~* /assets/favicon.*\.ico$ {
         alias /home/git/nginx/favicon-gdk.ico;
     }