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
* [x] Firefox support
* [x] iPad Support
* [x] Android support
  * [x] Chrome for Android -- works like desktop chrome
  * [x] Native Android Browser
* [x] IE Support
  * [x] IE11
  * [x] IE10
  * [x] IE9
  * [x] IE8 
* [x] Tests
So that actually brings up a good point. These buttons are the main place where we're actually consuming the new tracks API, whether native or custom. The buttons should show for both types of tracks, and should be able to update both types of tracks. So this is where you'll start to see all the discrepancies. They'll need to be re-written for the real text track workflow. For example, TextTrackMenuItem should stop using `showTextTrack`, and instead update the mode on the appropriate track. And then however we shim native tracks, the goal will be to make the buttons work as they do with the native tracks, without changing the buttons.