Periodic backups

[simongray]

The persisted storage (e.g. for comments #52) should be periodically backed up.

• The database should be backed up as a first step when restarting the Docker container
  • This is the most important backup as it guards against potential logic errors in updated versions of Glossematics. If an update goes wrong, the quickfix is to stop the container, revert to the backed up database, and restart the previous version.
• It should also be backed up every day or perhaps a few times a week.