Environment workaround

This client uses Python. This brings a major problem: In Python it is not possible to modify the environment of the parent process.
Because of this, hook scripts must use lmn-export and lmn-unset instead of export and unset. These scripts write the environment variables to a temporary file in ~/.linuxmuster-linuxclient7-environment.sh which is then sourced afterwards. This only works for the onLogin.d hook / the logon.sh script and is achieved in /etc/profile.d/99-linuxmuster-linuxclient7.sh which calls the onLogin script and sources ~/.linuxmuster-linuxclient7-environment.sh afterwards.