xfconf: add module

[chuangzhu]

Description

Add a module for Xfconf, the configuration system used by XFCE, similar to GNOME/GTK's dconf.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

  • Added myself and the module files to .github/CODEOWNERS.

[rycee]

Thanks! I've added a few comments.

[rycee]

Thanks! Merged to master now.

[pjones]

@chuangzhu I tried to use the new xfconf module but it doesn't look like it works:

hm-activate-pjones[4004]: Failed to init libxfconf: Cannot autolaunch D-Bus without X11 $DISPLAY.

This results in the home-manager activation failing. As far as I can tell there's no way to run xfconf-query without XFCE running.

Any suggestions?

[gou4shi1]

I meet the same issue as @pjones