Add tracks to texttrackdisplay on ready
Add tracks buttons async
Create custom tracks with the correct player
Move addTextTrack fully into techs.
Load up textTrackDisplay synchronously but have it do no work until the
player is ready (see the previous commit).
Move controlbar addition into player
In Html5, support tech, support non native tracks
Add a check that delegates to MediaTechController's methods if we're in
Html5 but we are not using native tracks.