fix: access on undefined variable

Implement picture in picture for iOS

Instead of crashing, show a warning and return

Throw an error instead of crashing app when video source is empty

fix: remove runtime warning by replacing `UIManager.RCTVideo` with `UIManager.getViewManagerConfig('RCTVideo')` (and ensuring backwards compat) (#1487)

* replaced UIManager.RCTVideo >  UIManager.getViewManagerConfig('RCTVideo')

* added requested changes

* updated changelog.md

* docs: adjust wording

* fix(ios): message sent to deallocated instance

* chore: update changelog

If an undefined source is accidentally loaded in react-native-video a fatal error SIGABRT will happen and crash the application. This is very difficult to debug since there's apparently no relation between this crash and react-native-video. So this change checks if the URI is empty and, if it is, it throws an error, allowing the user to find out early about the issue.

https://cloud.githubusercontent.com/assets/5795227/20283860/08223ba6-aabb-11e6-9fdc-d12d32b3aa9a.png

Feature Implementation: Recovery from transient internet failures

I'm guessing this change was made to cleanup the code, however it is not functionally identical and may cause issues. Revert until those can be discussed.

Support for displaying controls in Android Exoplayer

Defect fix: https://github.com/react-native-community/react-native-video/issues/1460

updated changelog for PR 1448

Doc modifications as per alplabetical order

Gradle changes reverted back

Doc changes for retry count implementation

Feature implementation: Failure Retry Count

Exoplayer gradle changes

Merge from master to my fork