Merge branch 'release-0.12.0' into master
Merge pull request #2537 from learningequality/release-0.12.0

Release 0.12.8
metadata for 0.12.8
Merge pull request #2742 from mrpau/hotfix/2271-Export-CSV-data-quality-issues

Hotfix/2271 export csv data quality issues
Revert "Hotfix/2271 export csv data quality issues"
Merge pull request #2747 from learningequality/revert-2742-hotfix/2271-Export-CSV-data-quality-issues

Revert "Hotfix/2271 export csv data quality issues"
Include Null in video_logs query for completion_timestamp .
Merge pull request #2762 from mrpau/hotfix/2271-Export-CSV-data-quality-issues

Hotfix/2271 export csv data quality issues.
Merge remote-tracking branch 'refs/remotes/upstream/master' into release-0.12.0
metadata for 0.12.9