Align the "logo" at the top.

This is visible on smaller screens (more specifically, when the links on
the right of the nav bar start wrapping and go to multiple lines, the
logo now stays at the top, instead of being vertically centered on the
nav bar).

content/layout/page.slab

@@ -9,13 +9,14 @@ frag page
     body.u-container-vertical
       header
         .u-container
-          .u-bar
+          .u-bar.u-bar--top-aligned
             .u-bar__left
               style.
                 .a-logo { color: black; text-decoration: none; }
-              a.a-logo(href="/")
-                div
-                  span.logo Slab
+              .menu-item-height
+                a.a-logo(href="/")
+                  div
+                    span.logo Slab
             .u-bar__right
               ul
                 li