Documentation for BackupNode component

There is a new configurable component called BackupNode in the configuration manager. It is a way to allow administrators to manage the backupnode process without using cron. Thor components now have an attribute called "enableBackupNode" that is defaulted to false. If this attribute is set to true, then the BackupNode component will add that thor cluster as a target to be backed up. Backup locations are defaulted to /var/lib/HPCCSystems/hpcc-data/backupnode/<thorname>/last_backup. The interval attribute of the BackupNode component determines how many hours between backups.