Ava test runner

[raineorshine]

Set up Ava testing with enzyme

• https://semaphoreci.com/community/tutorials/getting-started-with-create-react-app-and-ava

• https://shift.infinite.red/testing-the-bejeezus-out-of-react-native-apps-with-ava-330f51f8f6c3

[mekanix]

As Ava will support ES syntax starting with version 3, for now Jest is recommended test runner. For future reference, Enzyme official documentation about Ava setup is outdated. Also, adding babel presets didn't work as Ava transpiles only test files and uses CommonJS for the app.