Replace WebView from core with react-native-webview

[tchayen]

Due to the fact that WebView is about to leave React Native Core and was already move to a separate repository (see: https://github.com/react-native-community/react-native-webview), I have updated the import and added dependency.

More on the 'lean core' initiative: https://github.com/facebook/react-native/issues/23313

[jsamr]

@tchayen I'm not package author, but I have tried to port to community without success. Have you tried this code ?

I wonder if L71-73 are still relevant

[idealllee]

@scazzy It'd be great to have this change. Thanks for the library btw 👏