Add development helper script.

dev.sh

+#!/bin/sh
+
+case "$1" in
+    "install-all")
+	cd "$(dirname "$0")"
+	poetry install
+	for d in apps/official/*; do
+	    poetry run sh -c "cd $d; poetry install"
+	done
+	poetry run ./manage.py migrate
+	;;
+    *)
+	;;
+esac