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/main.scss

@@ -42,7 +42,8 @@
 @import 'components/banner';
 @import 'components/textbox';
 @import 'components/browse-list';
-@import 'components/switcher';
+@import 'components/management-navigation';
+@import 'components/dropdown';
 
 @import 'views/job';