so far, only renamed Backup to BackupManagers::ZipFileBackup
introduced BackupManager
work in progress
Merge branch 'master' into refactor-backup

Conflicts:
	indie-box/vendor_perl/IndieBox/BackupManagers/ZipFileBackupManager.pm
	indie-box/vendor_perl/IndieBox/Site.pm
distinguish between backups made for admin purposes (e.g. code upgrades), test purposes (indie-box-testing) and by the user for other purposes.
removed unnecessary import
updated readme
fixed typo