Support Kotlin for Android

[brody4hire]

parallel to supporting Swift for iOS as requested in #221

Here are some interesting resources I discovered from https://www.google.com/search?q=react+native+kotlin:

• https://levelup.gitconnected.com/powering-react-native-with-kotlin-swift-support-e5c1210a4e25
• https://callstack.com/blog/writing-a-native-module-for-react-native-using-kotlin/
• https://proandroiddev.com/react-native-bridge-with-kotlin-b2afde2f70b
• https://github.com/guardian/react-native-with-kotlin

I do think it would be ideal to get general Swift & Kotlin built into the React Native template (someday).