When the video duration is unknown, fetch it from a YouTube API.

Before this change, when using the HTML5 player on the preview page, question
icons would not render at the correct position because duration was zero.

Test plan:
Turn on YouTube HTML5 player, and open http://localhost:8000/editor/index.html.
Observe that question icons are correctly positioned.
Improve timings for video
Remove old templateName code, templates are now inlined
Merge branch 'master' of github.com:dmnd/socrates