Docker: Reduce image layers and improve build scripts

scripts/dist/install-nodejs.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+
+# abort if the user is not root
+if [[ $(id -u) != "0" ]]; then
+  echo "Usage: run install-nodejs.sh as root" 1>&2
+  exit 1
+fi
+
+set -e
+
+SETUP_URL="https://deb.nodesource.com/setup_16.x"
+
+echo "Installing NodeJS and NPM from \"$SETUP_URL\"..."
+
+curl -sL $SETUP_URL | bash -
+apt-get update && apt-get -qq install nodejs
+npm install --unsafe-perm=true --allow-root -g npm
+npm config set cache ~/.cache/npm
+
+echo "Done."