[MIG] account_xunnel:Migration to v18.0

Changelog:

Security:
- Use Command syntax.

Models:
- Change in _open_iframe_   method in account_online_link model,
  increasing the number of required parameters,  last change in this method[1].

Tests:
- Updated tests to use `setUpClass` instead of `setUp` for better efficiency.

I18n:
- Regenerate translations.

[1]: https://github.com/Vauxoo/enterprise/commit/09c54e7