Support native captions in html5 tech.

Don't auto-add the textTrackDisplay component.
Add a 'featuresNativeTrack'. Currently hardcoded to false for everything
except the html5 tech.
Add textTracks and addTextTrack methods to html5 tech.
Proxy player level methods to tech if we're using native tracks.
Fix up track menu items to work with spec tracks or vjs tracks.

This is the beginning of step 1 for the [revamp](https://github.com/videojs/video.js/issues/1655) of text tracks.

* [x] Native tracks, if available
* [x] Re-use non-native otherwise
* [x] Chrome Support
* [ ] Firefox support
* [x] iPad Support
* [ ] Android support
* [ ] Tests
we should probably use textTrack instead of just tracks here, because of videoTracks and audioTracks