Extract the database connection handling from the server

Previously, one of the first things that happened when responding to a request
was a database connection was made, even when serving the CSS. This is
unnecessary, so move the database connection handling in to the controller.

Also, to allow for separating it out from the assets, separate the assets out
from the parts of the controller that require a database connection.

guix-data-service/web/server.scm

@@ -23,22 +23,18 @@
   #:use-module (web request)
   #:use-module (web uri)
   #:use-module (fibers web server)
-  #:use-module (guix-data-service database)
   #:use-module (guix-data-service web controller)
   #:use-module (guix-data-service web util)
   #:export (start-guix-data-service-web-server))
 
 (define (run-controller controller request body)
-  (with-postgresql-connection
-   (lambda (conn)
-     (let-values (((request-components mime-types)
-                   (request->path-components-and-mime-type request)))
-       (controller request
-                   (cons (request-method request)
-                         request-components)
-                   mime-types
-                   body
-                   conn)))))
+  (let-values (((request-components mime-types)
+                (request->path-components-and-mime-type request)))
+    (controller request
+                (cons (request-method request)
+                      request-components)
+                mime-types
+                body)))
 
 (define (handler request body controller)
   (format #t "~a ~a\n"