Started on a design update

- Added base of new grid system.
- Added new margin/padding/visiblity helpers.
- Made header collapse to overflow menu on mobile.

resources/assets/js/components/index.js

@@ -20,6 +20,7 @@ let componentMapping = {
     'page-display': require('./page-display'),
     'shelf-sort': require('./shelf-sort'),
     'homepage-control': require('./homepage-control'),
+    'header-mobile-toggle': require('./header-mobile-toggle'),
 };
 
 window.components = {};