Docker support for production use

This commit adds a Docker infrastructure that is ready for production
use. It is meant to simplify the deployment of OSEM for everyone who
wants to host their own instances.

It includes many features like data persistence, automatic secret key
generation and persistence and automatic database initialization and
upgrading. This should make updating the Docker container as easy as
possible.

docker/init.sh

@@ -0,0 +1,45 @@
+#! /bin/bash
+
+set -e
+
+# data directory is required for caching the secret key in a file
+if [ "$DATA_DIR" == "" ]; then
+    echo -n "Error: DATA_DIR environment variable not set!"
+    echo "Are you sure you are running this script in a Docker container?"
+    exit 1
+fi
+
+SECRET_KEY_FILE="$DATA_DIR/secret_key"
+
+if [ ! -f "$SECRET_KEY_FILE" ]; then
+    install -m 0600 /dev/null "$SECRET_KEY_FILE"
+    SECRET_KEY=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 100 | head -n 1)
+    echo "$key" > "$SECRET_KEY_FILE"
+    chmod -w "$SECRET_KEY_FILE"
+else
+    SECRET_KEY=$(cat "$SECRET_KEY_FILE")
+fi
+
+export SECRET_KEY
+export RAILS_ENV=production
+
+install -m 0600 /dev/null .my.cnf
+cat > .my.cnf <<ABC
+[client]
+user=$MYSQL_USER
+password=$MYSQL_PASSWORD
+ABC
+
+if [ $(echo "show tables;" | mysql --host $DATABASE_HOST --port $DATABASE_PORT $MYSQL_DATABASE | wc -l) -le 1 ]; then
+    echo ">>> Initializing database..."
+    dockerize -wait tcp://$DATABASE_HOST:$DATABASE_PORT -timeout 60s bundle exec rake db:schema:load
+fi
+
+echo ">>> Upgrading database..."
+dockerize -wait tcp://$DATABASE_HOST:$DATABASE_PORT -timeout 60s bundle exec rake db:migrate
+
+echo ">>> Precompiling assets..."
+bundle exec rake assets:precompile
+
+echo ">>> Starting application server..."
+exec puma -e production