* gnu/services/web.scm (config-domain-strings, config-index-strings): Emit
lists instead of strings.
(emit-nginx-location-config, emit-nginx-server-config)
(emit-nginx-upstream-config): Rename from nginx-location-config,
default-nginx-server-config, and nginx-upstream-config. Emit lists instead of
strings.
(flatten): New helper.
(default-nginx-config): Use flatten helper to write nginx conf. This allows
location configs to reference store values.
Signed-off-by: Christopher Baines <mail@cbaines.net>