Move appearance settings as sub tab to application settings

app/views/admin/appearances/show.html.haml

+- @no_container = true
 - page_title "Appearance"
-%h3.page-title
-  Appearance settings
-%p.light
-  You can modify the look and feel of GitLab here
+= render "admin/application_settings/head"
 
-= render 'form'
+%div{ class: (container_class) }
+  .prepend-top-default
+    = render 'form'

app/views/admin/application_settings/_head.html.haml

+.nav-links.sub-nav
+  %ul{ class: (container_class) }
+    = nav_link(controller: :application_settings) do
+      = link_to admin_application_settings_path, title: 'Settings' do
+        %span
+          General
+
+    = nav_link(controller: :appearances) do
+      = link_to admin_appearances_path, title: 'Appearances' do
+        %span
+          Appearance

app/views/admin/application_settings/show.html.haml

+- @no_container = true
 - page_title "Settings"
-%h3.page-title Settings
-%hr
-= render 'form'
+= render "admin/application_settings/head"
+
+%div{ class: (container_class) }
+  .prepend-top-default
+    = render 'form'

app/views/layouts/nav/_admin.html.haml

@@ -21,11 +21,6 @@
       %span
         Hooks
 
-  = nav_link(controller: :appearances) do
-    = link_to admin_appearances_path, title: 'Appearances' do
-      %span
-        Appearance
-
   = nav_link(controller: :applications) do
     = link_to admin_applications_path, title: 'Applications' do
       %span
@@ -53,7 +48,7 @@
         %span
           Spam Logs
 
-  = nav_link(controller: :application_settings, html_options: { class: 'separate-item'}) do
+  = nav_link(controller: [:application_settings, :appearances]) do
     = link_to admin_application_settings_path, title: 'Settings' do
       %span
         Settings