Relocating some procedures into (guix utils)

[Bruno Victal]

IMO there are some procedures (or even modules) that could be relocated into 
(guix utils) as their utility is more general than what their module names 
would suggest.

Good candidates to relocate into (guix utils):
* (gnu home services utils)
* list-of, interpose, alist?, list-of-string? from (gnu services configuration)

The procedures above are general enough and it's not hard to imagine that some 
of these could be useful in package definitions.


Cheers,
Bruno