Add a simple backup server software release.

Request the service with the software type pullrdiffbackup.

Real backup are added by request a slave with required parameters:
  hostname="example.org" (just to make think readable for human)
  connection="user@0.0.0.0" (ssh connection string)
  include="/src /home" (space separated directory path to backup)
  frequency="0 0 * * *" (crontab like periodicity string)

Optional parameters are:
  exclude="/home/userA /home/userB" (space separated directory path to not backup)
  sudo="True" (if the server to backup contains a local backupagent_rdiff-backup script which is callable with sudo)