BLD-237: Persist speed preferences between videos.

CHANGELOG.rst

common/lib/xmodule/xmodule/js/fixtures/video.html

common/lib/xmodule/xmodule/js/fixtures/video_all.html

common/lib/xmodule/xmodule/js/fixtures/video_html5.html

...on/lib/xmodule/xmodule/js/fixtures/video_no_captions.html

...on/lib/xmodule/xmodule/js/fixtures/video_yt_multiple.html

common/lib/xmodule/xmodule/js/spec/helper.js

.../lib/xmodule/xmodule/js/spec/video/cookie_storage_spec.js

common/lib/xmodule/xmodule/js/spec/video/general_spec.js

...on/lib/xmodule/xmodule/js/spec/video/video_player_spec.js

...xmodule/xmodule/js/spec/video/video_speed_control_spec.js

common/lib/xmodule/xmodule/js/src/video/00_cookie_storage.js

common/lib/xmodule/xmodule/js/src/video/01_initialize.js

common/lib/xmodule/xmodule/js/src/video/03_video_player.js

common/lib/xmodule/xmodule/js/src/video/09_video_caption.js

common/lib/xmodule/xmodule/video_module.py

lms/djangoapps/courseware/features/video.feature

lms/djangoapps/courseware/features/video.py

lms/djangoapps/courseware/tests/test_video_mongo.py

lms/djangoapps/courseware/tests/test_video_xml.py