Uses environment variables instead of hard coding the "deck" user/group.
This adds support for systems other than the steam deck that are using the DeckUI.

* Use Environment Variables

* Use method to get USER from a systemd root process

* Fix imports. Add get_user and get_user_group methods in helpers.py. Removed duplicated code

* Add separate setters/getters for user vars. Ensure sleep prevents race condition of user setter in while loop