Move constants to `Constants.js`

app/assets/javascripts/protected_tags/index.js

 export { default as ProtectedTagCreate } from './protected_tag_create';
 export { default as ProtectedTagEditList } from './protected_tag_edit_list';
-
-export const ACCESS_LEVELS = {
-  CREATE: 'create_access_levels',
-};
-
-export const LEVEL_TYPES = {
-  ROLE: 'role',
-  USER: 'user',
-  GROUP: 'group',
-};
-
-export const ACCESS_LEVEL_NONE = 0;