Wrap RNTwitterKit with a plain JS view class and provide propTypes.

[ognen]

The RNTwitterKit native module should be wrapped with a pure JS react component called TweetView.

This allows propTypes to be declared and documented in a way that is understandable for the JS users
of the library.

TweetView should be the default export of the index.js.

See https://facebook.github.io/react-native/docs/native-components-ios.html#properties

[andianton]

• done in iOS