safe backup command

[jhunt]

Here's what I want to do:

$ safe backup
backup export saved to secret/safe/backups/20180322.093414-jhunt

$ safe restore secret/safe/backups/20180322.093414-jhunt
Are you sure you want to restore? [yn] y
successfully restored backup.

$ safe backup secret/special
backup export saved to secret/safe/backups/20180322.093522-jhunt

etc.

It would be nice if the restore would do an analysis and determine if (a) it's going to run into permissions issues and (b) if it's going to remove things that aren't in the backup. Perhaps a --full option to restore?