[Forwardport] Inconsistent Redirect in Admin Notification Controller

[dimonovp]

Original Pull Request

#13828

This controller has an inconsistent redirect mechanism (than other controllers in admin-notification). This means that if the admin has a different URL, the admin user is returned to the frontend URL of the default store instead.

Manual testing scenarios

1. Setup admin to run on a separate domain to the main site
2. Attempt to mass remove all notifications within admin

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)