Add Arch package groups

[chrisduerr]

It would be convenient if the public Arch repo had a package group available, making it possible to get a basic Catacomb setup going without having to know which software to pick.

Ideally there'd be two different configs, one "medium" bloated one that just installs Catacomb/Epitaph/Tzompantli to get the basic stuff going, while the other fully bloated one installs Kumo, Alarm, Settings, etc.

In theory Arch package groups even have the option to provide alternatives, so it would be possible to even suggest alternatives where available.