Re-export classes using ES6 `export`

app/assets/javascripts/protected_tags/index.js

-require('./protected_tag_access_dropdown');
-require('./protected_tag_create');
-require('./protected_tag_dropdown');
-require('./protected_tag_edit');
-require('./protected_tag_edit_list');
+export { default as ProtectedTagAccessDropdown } from './protected_tag_access_dropdown';
+export { default as ProtectedTagCreate } from './protected_tag_create';
+export { default as ProtectedTagDropdown } from './protected_tag_dropdown';
+export { default as ProtectedTagEdit } from './protected_tag_edit';
+export { default as ProtectedTagEditList } from './protected_tag_edit_list';