Update backup.sh

Added ability to delete backups from the backup FTP after X days.
Added ability to delete local files after the transfer to the backup FTP is completed successfully.
Users can now define the home directory.
Fixed a bug that weren't copying all the files successfully to the FTP
Added Passive mode while connecting to FTP

NOTE: The date format that is stored on the backup FTP has been changed from MM-DD-YYYY to YYYY-MM-DD