Add database-independent backup format support
It might make sense to support a database-type independent backup for Postfix (and release a standard/writeup of the contents?). This could make it easier to transition from a SQLite powered backend to a Postgres powered one, should the need ever arise -- it seems like if a DB is created but then the user decides to switch to Postgres instead there would be no way to migrate all the data -- would be nice if they could just disconnect, dump, change settings, reconnect and trigger a restore from backup