Remove app.search instance, cache app.cache.searched (#2151)

* Moved search state logic into search state

js/src/forum/ForumApplication.js

@@ -1,6 +1,5 @@
 import History from './utils/History';
 import Pane from './utils/Pane';
-import Search from './components/Search';
 import ReplyComposer from './components/ReplyComposer';
 import DiscussionPage from './components/DiscussionPage';
 import SignUpModal from './components/SignUpModal';
@@ -15,6 +14,7 @@ import alertEmailConfirmation from './utils/alertEmailConfirmation';
 import Application from '../common/Application';
 import Navigation from '../common/components/Navigation';
 import NotificationListState from './states/NotificationListState';
+import GlobalSearchState from './states/GlobalSearchState';
 
 export default class ForumApplication extends Application {
   /**
@@ -35,13 +35,6 @@ export default class ForumApplication extends Application {
     discussionRenamed: DiscussionRenamedPost,
   };
 
-  /**
-   * The page's search component instance.
-   *
-   * @type {Search}
-   */
-  search = new Search();
-
   /**
    * An object which controls the state of the page's side pane.
    *
@@ -71,6 +64,14 @@ export default class ForumApplication extends Application {
    */
   notifications = new NotificationListState(this);
 
+  /*
+   * An object which stores previously searched queries and provides convenient
+   * tools for retrieving and managing search values.
+   *
+   * @type {GlobalSearchState}
+   */
+  search = new GlobalSearchState();
+
   constructor() {
     super();