When directory structure was refactored, source files were moved to `ios/` dir, but the podspec wasn't updated to reflect this.

* offered html5-like poster attribute

* prevent unnecessary setState

feat(Windows): Adds Windows support to react-native-video

This PR adds react-native-windows support to react-native-video.  The Video component is implemented with a XAML MediaPlayerElement.  Most of the features implemented by Android (and some additional ones) are implemented by Windows.

Known issues and missing features include:
* onReadyForDisplay event
* local URI convention (e.g., "broadchurch" in examples changed to require("./broadchurch.mp4")
* `playableDuration` in `onVideoProgress` event is always 0.0
* `playInBackground` is not yet supported
* Volume settings are applied, but the UWP control does not handle it properly

* BUGFIX. Progress Update Handler was being called even when the video was paused. The handler was also being called unnecessarily even after the video has completed and unmounted

* Saved and restored the state of the video during the activity state changed

* added progressUpdateInterval prop iOS

* add prop to Video.js

* added progressUpdateInterval prop iOS

* add prop to Video.js

Similar to #153, attempts to pause in fullscreen mode will be negated by the `playbackLikelyToKeepUp` event.

This PR adds a check for `_fullscreenPlayerPresented`, in additional to `_controls` before calling `setPaused` for `playbackLikelytoKeepUp`.

This update is likely preferrable to #258, as it doesn't lose the empty buffer check.

* Add Android Expansion File Support

* Added notes for usage with Android Expansion file

* Update README.md

Added notes re: expansion file usage.

* formatting issue fixes

Added deallocation of observers

Add controls property to Android

use react native asset resolving