Merge pull request #3253 from kepstin/recording-captions

record-and-playback/core/lib/recordandplayback.rb

record-and-playback/core/scripts/utils/gen_webvtt

...ntation/0.9.0/acornmediaplayer/jquery.acornmediaplayer.js

...back/presentation/playback/presentation/0.9.0/playback.js

...and-playback/presentation/scripts/process/presentation.rb

...and-playback/presentation/scripts/publish/presentation.rb