Run a backup as part of the update command

[velovix]

When doing an update, there's always the risk that a buggy or interrupted migration could compromise the integrity of the database. When doing a downgrade, which we don't officially support, data integrity issues are very likely. We should always do backups before an update to give the user an out if something happens, perhaps with a flag to disable it if the user is sure they know what they're doing.

[apockill]

Yes I think this is a great idea!