iOS Side loading for captions and offline support

clearSelectionOverride is still required for "default" and "disabled" case as it otherwise continues to show a selected track if it was previously selected

# Conflicts:
#	ios/RCTVideo.m
#	package.json

Show iOS controls without using present full screen

fix to respect User settings for captions.

Update README.md

fix small grammar mistake

Disable HTTP headers on iOS since it uses a private API

ExoPlayer playableDuration incorrect

Prevent iOS onLoad event during seeking

added optional request headers for remote assests (android & ios)

adds supported file extensions Android Expansion files