Add backup/restore

Re coop-cloud/organising#30

abra.sh

@@ -1 +1,13 @@
 export ENTRYPOINT_CONF_VERSION=v1
+
+abra_backup_app() {
+  _abra_backup_dir "app:/home/hackmd/app/public/uploads/"
+}
+
+abra_backup_db() {
+  _abra_backup_postgres "db" "codimd" "codimd" "db_password"
+}
+
+abra_backup() {
+  abra_backup_app && abra_backup_db
+}