Need backup/restore command

[dchassin]

The server command needs a backup and a restore option.

[dchassin]

Backup requirements

1. The backup command should commit an image based on the current state of the container (default container name is openfido-server-1).
2. The default name of the image should openfido-backup-YYMMDD-HHMMSS.
3. The most recently saved image should also be named openfido-backup-latest.
4. The image should save the image to a tar file using the same base name for archival.
5. Once the tar file is saved, any older images may be removed to save space.
6. If there is insufficient space to save the image, then older tar files may be removed.
7. The most recently saved image should be kept until a newer one is committed.

Restore requirements

1. The restore command should restore the most recently saved image.
2. If an image name is provided, then the named image should be restored.
3. If a server is active, then the restore command should fail, unless the --force option is provided.