graphical installer

[ng0]

Hi,

I'm setting up a guix developer machine after a really long time
without one.
One instant feedback on the installer: it would be nice to have
a territory "Other" or just any continent and country combination
(in the Locale step).
My motivation is that I usually have an en_US.UTF-8 locale in
Germany. I don't think it's a common case, but I think I'm not
a special exception.

I could use the old way to install Guix System, but I wanted to
try out the improvements which might've happened in my inactive
time :)