Add video.js as YouTube fallback player
Ensure tab parameters survive player swap
Refactor fallback callback
Add instructions for browserstack testing of YouTube fallback
Add explicit fallback player width for IE9. Prefer Flash player for IE9.
Add notes on testing production locally
Clean up video.js player on modal close. Give video.js players unique IDs. Add thumbnail info to video links.
Merge pull request #472 from code-dot-org/youtube_fallback

Add YouTube fallback