Fixed the path to dms-colors.json, as the previous path did not actually exist, resulting in a broken symbolic link and the colors not actually being right in the login screen.
* add nixos support for greeter
* fix greeter config file access
* fix wallpaper perms and allow for adding extra compositor config
* fix greeter config files ownership
* set default for compositor.extraConfig
* update option docs about copying instead of symlinking
* explain configHome in doc further
* add nixos option to redirect greeter logs
* prevent possible errors in greetd preStart