Minor fixes for 3.2

OnApp PHP Wrapper version 3.2.0 fixes (for OnApp version 3.2.2)
** User/Statistics.php - Added 2 fields to get user backups cost: 
a) backup_count_cost - cost per backup per hour for the backups of a particular Backup server zone.
b) backup_disk_size_cost - cost per GB per hour for the backups of a particular Backup server zone.

** VirtualMachine/Backup.php - defined ONAPP_GETRESOURCE_ENABLE_BACKUP for auto-backups. Implemented enableAutoBackup() method

** VirtualMachine/BillingStatistics.php - Changed $_tagRoot to vm_hourly_stat and fixed getList() method to get shorter statistics output