added type doc to menu related files

src/app/shared/menu/menu-item/models/text.model.ts

@@ -0,0 +1,10 @@
+import { MenuItemType } from '../../initial-menus-state';
+import { MenuItemModel } from './menu-item.model';
+
+/**
+ * Model representing an Text Menu Section
+ */
+export class TextMenuItemModel implements MenuItemModel {
+  type = MenuItemType.TEXT;
+  text: string;
+}