nginx: normalize installation (docs and script)s over all distros

This is the revision of the documentation about the varous nginx installation
variants.  It also implements the nginx installation scripts for morty and
filtron.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

utils/templates/etc/nginx/default.apps-available/morty.conf

@@ -0,0 +1,11 @@
+# https://example.org/morty
+
+location /morty {
+    proxy_pass         http://127.0.0.1:3000/;
+
+    proxy_set_header   Host             \$http_host;
+    proxy_set_header   Connection       \$http_connection;
+    proxy_set_header   X-Real-IP        \$remote_addr;
+    proxy_set_header   X-Forwarded-For  \$proxy_add_x_forwarded_for;
+    proxy_set_header   X-Scheme         \$scheme;
+}