This PR changes the following:

• After idling too long, the user session is now terminated using loginctl instead of relying on lightdm to terminate the session properly. Afterwards the display manager is still restarted to prevent bug Screen unlock crashes a session after a forced logout from the systemd idling script #7 from reappearing.
• After logging the user out, the idle logout service will now check for a script /usr/share/codam/codam-web-greeter-idler-hook.sh to exist. If it exists, it is executed. This allows for custom functionality to be added upon idle logouts, such as a deduction in coalition points, more logging or automated notifications.