Feature/april changes 2 (#450)
* Refactored Android notification image selection.
* Refactored Android notification image selection.
* Updated example
* Added headers parameter in BetterPlayerSubtitlesSource
* Added headers parameter in BetterPlayerSubtitlesSource
* Added activityName, open application on notification click on Android
* Fixed playing only audio data sources in iOS
* Fixed playing only audio data sources in iOS
* Removed invalid files
* Updated changelog
* Updated Exo Player version
* Fixed notification not updating correctly for playlists in Android.
* Fixed notification not updating correctly for playlists in Android.
* Removed deprecated Android code. Better Player supports now only v2 embedding.
* Removed deprecated Android code. Better Player supports now only v2 embedding.
* Updated version
