Add support for building ubuntu:20.04-based docker images + some automation

build-docker-images.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+
+prefix="${1:-local/}"
+
+for dokerfile in dockerfiles/Dockerfile.* ; do
+    suffix="`echo "$dokerfile" | sed 's/.*\/Dockerfile\.//'`"
+    image_name="${prefix}zeronet:$suffix"
+    echo "DOCKER BUILD $image_name"
+    docker build -f "$dokerfile" -t "$image_name" .
+done