Moved site dependent variables out of the rman_bck.sh script

Moved the site dependent variables out of the rman_bck.sh script to the global_var.par file.
This makes it easier to perform upgrades and more clear which variables have to be set when deploying a new client
added some more explanation in the README.md file
Merge remote-tracking branch 'origin/dev' into move_site_var
Modified the documentation in the README.md