Simplify navbar implementation - this will also allow seamlessly adding a third, centred nav if desired

src/Foundation.hs

@@ -97,8 +97,7 @@ instance Yesod App where
         -- Get the breadcrumbs, as defined in the YesodBreadcrumbs instance.
         (title, parents) <- breadcrumbs
 
-        let navbarLeftMenuItems = leftMenuItems muser
-            navbarRightMenuItems = rightMenuItems muser
+        let navbars = [leftMenuItems, rightMenuItems] <*> [muser]
 
         -- We break up the default layout into two components:
         -- default-layout is the contents of the body tag, and