Bug fixes

The unintended removal of deleted configuration files is fixed.

Applied some minor bug fixes and corrected usage of deprecated functionality for Drupal 9 compatibility.

Tether Stats can now be installed on Drupal 9.

Commits in this release:

1. Removed all debug messages
2. Added README.md
3. Added missing config schema
4. Applied Drupal coding standards
5. Removed default role-menu pair
6. Updated deprecations to make module ready for Drupal 9

This is a beta release for the final, long-term support minor version of Drupal 8. Beta releases are good testing targets for developers and site builders who are comfortable reporting (and where possible, fixing) their own bugs. Beta releases are not recommended for non-technical users, nor for production websites. More information on beta releases.

Fixed contextual issue and found some deprecated code.

Issue #3119862 by mferanda, mortona2k: 2.3 Testing - Issue with contextual links
Issue #3136772 by mferanda: Use 2.7.0 for demo USWDS style links
Issue #3136771 by mferanda: Deprecated code

- Add core_version_requirement: ^8 || ^9 to scrollbar.info.yml to designate that the module is compatible with Drupal 9.
- Deprecated method drupal_set_message() is removed.