bugfix: unmounting a package could lead to a deletion of services used in other packagesA new API call "site_node::unmount_services" can be used to unmount all services in a first step.unmount services before calling "site_node::delete -node_id $node_id -delete_subnodes -delete_package"prevents collateral damage.
Replace occurrences of exists_and_not_null with plain tcl idioms, as the goal is to deprecate this proc shortlyThis required an upgrade script as some code is actually stored in the database