Avoid crash when there are no tracks to choose from

Fix missing TargetApi 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

[WIP] Update ExoPlayer to version 2.8.2

Feat/ontimedmetadata android

ios Caching Support