Support conf.nativesubtitles (#85)
Support conf.nativesubtitles (#85)

At the price of destroying the hls instance and the video tag on
playlist switch if textTracks were present.

A less brutal approach is thwarted by the following scenario:
- default track of next clip has same language or label as a track in
  the previous clip
- hls.js recognizes it, listing it in subtitleTracks, but it is not
  present in textTracks

flowplayer/flowplayer-hlsjs