PLT-4457 Added AtMention component to better render at mentions (#6563)

* Moved Utils.searchForTerm into an action

* Added easier importing of index.jsx files

* PLT-4457 Added AtMention component to better render at mentions

* Fixed client unit tests

* Fixed merge conflict

* Fixed merge conflicts

webapp/actions/post_actions.jsx

@@ -351,3 +351,11 @@ export function increasePostVisibility(channelId, focusedPostId) {
         return posts.order.length >= POST_INCREASE_AMOUNT;
     };
 }
+
+export function searchForTerm(term) {
+    AppDispatcher.handleServerAction({
+        type: ActionTypes.RECEIVED_SEARCH_TERM,
+        term,
+        do_search: true
+    });
+}