Adding support for movies subtitles.

Subtitles are fetched from api.yifysubtitles.com.
videojs player is now built dynamically in order to properly load subtitles.

Subtitles are placed in public/subtitles folder, allowing videojs to fetch them from http://hostname:4000/subtitles/language.srt
Subtitles are removed only when the user kill a stream.

Srt files not encoded in UTF-8 are not displayed correctly, should we convert them ?

This fixes  #9