Show nicely formatted subtitles

[justinsilvestre]

The default HTML5 video subtitles were made to show one track at once. So if two subtitles tracks are turned on, they won't be displayed in a consistent way, i.e. sometimes English subtitles will be above Japanese subtitles, and sometimes vice-versa.

It would be nice to see the content of subtitles nicely formatted, as in the flashcard view, even when a flashcard hasn't been made at that point in a video. This would make Knowclip useful for simply watching videos with dual subtitles tracks, even without making any flashcards.

[justinsilvestre]

Inadvertently implemented this on the way to implementing the cloze deletion feature #42