Bug fixes

We decided to extend the the support of 8.x-1.x until 2020-12-31. This should be enough time to upgrade to 4.x.

This release modifies the update checks accordingly and adjusted the tests to succeed against Drupal 8.8 and 8.9.
The minimal support throughout 2020 will NOT cover

Remove Drupal 9 support form the info file as we will support D 8.8+ and D9 with the 4.0.x branch only, see #3134576: Included modules need core_version_requirement key

Fixes a few bugs and make the module D9 compatible:
#3098318: Remove usage of deprecated drupal_set_message
#3098359: Missing configure button in module listing page

Initial functional version for D8 and D9

Deprecations removed
Allow Multiple Boolean Field Values to be passed in the Site Settings Loader
Move definition of cache BIN/CID constants into class rather than in the .module file

Drupal 9 compatibility