Add published method on VersionTracker queryset

Co-Authored-By: Gavin Wahl <gwahl@fusionbox.com>
PEP-8 compliance fix
Refactor tests in order to use custom widgy sites
Add test for VersionTracker.objects.published()
Merge remote-tracking branch 'origin/get-publish-commits'

* origin/get-publish-commits:
  Add test for VersionTracker.objects.published()
  Refactor tests in order to use custom widgy sites
  PEP-8 compliance fix
  Add published method on VersionTracker queryset