How does it work?
- creates backup directory under the ownCloud data directory.
- extracts update package content into the backup/packageVersion
- makes the copy of the current instance (except data dir) to backup/currentVersion-randomstring
- moves all folders except data, config and themes from the current instance to backup/tmp
- moves all folders from backup/packageVersion to the current version
- copy old config.php to the config directory.
