Restore XFCE theming

[zardus]

The nix move removed our custom awesome theming (e.g., there's no a panel at the bottom). Let's get our theming back.

[zardus]

@spencerpogo is this something you'd have time to do?

[spencerpogo]

Sure, I'll try and get nix to pick up the .xmls

[ConnorNelson]

@spencerpogo Ideally we don't cp files into the home directory to achieve this. We already have some level of configuration that works with the files just existing in nix, and the goal would be to get more of those files in.