Adds support to run processes as a user/group, defined

with PUID and PGID environment variables

- Detects if image is run with a user in docker command and fails if so
- Adds s6 prepare scripts for adding a 'npmuser'
- Split up and refactor the s6 prepare scripts
- Runs nginx and backend node as 'npmuser'
- Changes ownership of files required at startup

docker/rootfs/bin/common.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+set -e
+
+CYAN='\E[1;36m'
+BLUE='\E[1;34m'
+YELLOW='\E[1;33m'
+RED='\E[1;31m'
+RESET='\E[0m'
+export CYAN BLUE YELLOW RED RESET
+
+log_info () {
+	echo -e "${BLUE}❯ ${CYAN}$1${RESET}"
+}
+
+log_error () {
+	echo -e "${RED}❯ $1${RESET}"
+}
+
+# The `run` file will only execute 1 line so this helps keep things
+# logically separated
+
+log_fatal () {
+	echo -e "${RED}--------------------------------------${RESET}"
+	echo -e "${RED}ERROR: $1${RESET}"
+	echo -e "${RED}--------------------------------------${RESET}"
+	/run/s6/basedir/bin/halt
+	exit 1
+}