[MIG] invoice_xunnel: Migration to v18.0

Changelog:

Models:
- Remove  `documents_workflow_rule` model since it was removed and now
  workflows are converted to `documents`-linked `ir.actions.server` and
  can be configured to link a document to any model check this commits
  for reference [1][2].

Assets:
- Document inspector no longer exists in 18.0 check this commit for
  reference [2].
- Library notify.min.js used to display an alert when an item of a xml
  is selected was replaced by the use of notification service native in
  Odoo.

Tests:
- In past versions `test_controller_main` had an error at getting
  acces_token in httprequest.args. Now we asigned an example token to
  the mock request to prevent this error.
- Folder creation is now done in `documents.document` model.
- Some test were updated to use `setUpClass` method instead of `setUp`
  for better performance.

Views:
- Changes in xpath expressions in `documents_views.xml` since
  document_view_kanban change its structure.

I18n:
- Regenerate translations.

[1]: https://github.com/Vauxoo/enterprise/commit/1d11b642
[2]: https://github.com/Vauxoo/enterprise/commit/a32825e