Add progressive enhancement to service switcher

- by default, the menu is open
- if Javascript is enabled/loaded, the links are hidden, and visual cues (▶) to
  show that it can be opened are added
- clicking it opens and closes it

app/assets/stylesheets/components/management-navigation.scss

@@ -0,0 +1,27 @@
+.management-navigation {
+
+  @extend %site-width-container;
+  @include core-16();
+  border-bottom: 1px solid $border-colour;
+  padding: 10px 0 8px;
+
+  a:link,
+  a:visited {
+    text-decoration: none;
+  }
+
+  &-account {
+
+    @include media(tablet) {
+
+      text-align: right;
+
+      a {
+        margin-left: 20px;
+      }
+
+    }
+
+  }
+
+}