Merge pull request #2254 from learningequality/release-0.12.0

Release 0.12.2
Hot fix for #1985 to make `generaterealdata` management command work.
Hot fix to pass Travis tests by checking that `lang_name` has a value for dubbed video data on `get_dubbed_video_map()`.
Also includes hot fix related to #1253.
This overrides the previous commits os similar-named branch to cherry-pick final codes to remove the debug commits.
Remove hot fix because json is fixed on central server.
Merge pull request #2270 from cpauya/feature/1985-generaterealdata-fails-in-model-generation-2

Hot fix for #1985 to make `generaterealdata` management command work.
Merge branch 'master' of github.com:learningequality/ka-lite into release-0.12.0