Update to ExoPlayer 2.8.4

Add support for react-native-dom

Remove flash between poster and video

Reduce package size

Remove unnecessary import in TextTrackType.js

Avoid crash when there are no tracks to choose from

Fix missing TargetApi import

Remove not needed import

The build was producing a "cannot find symbol class TargetApi" error without that line.

add ipod-library support

Couldn't figure out how this was happening, so I don't want to hide it with try/catch. Let's get it fixed instead.

Merge caching changes into master

[WIP] Prevent errors on iOS when using text tracks with caching

Fixes a crash when using the cache & sideloaded text tracks together due to the tracks on the asset not being available. Re-visit when someone with more expertise on the cache can look at it.

Reorganize README