React Native Web3.js example

Example on how to run web3js with Expo tool chain. There is not much at the moment beside being able to import web3 and display accounts available on the links page

To Know

• It use the pure JavaScript implementation of Web3, see reference in services/web3/VERSION.
• Web3 require btoa method to be available globally, I add the implementation in global.js and import it at the top of App.js.
• bn.js and indexof are needed too.