Require search dropdown class in search container.

Previously it happened to be required by search controller.
But one shouldn't rely on such a coincidence - each view should
declare all the classes it depends on.

template/app/controller/Search.js

@@ -9,10 +9,6 @@ Ext.define('Docs.controller.Search', {
         'Docs.History'
     ],
 
-    views: [
-        'search.Dropdown'
-    ],
-
     stores: ['Search'],
 
     refs: [

template/app/view/search/Container.js

@@ -4,6 +4,7 @@
 Ext.define('Docs.view.search.Container', {
     extend: 'Ext.container.Container',
     alias: 'widget.searchcontainer',
+    requires: 'Docs.view.search.Dropdown',
 
     initComponent: function() {