Switch from preset-latest to preset-env

Created by: Timer

We should probably switch babel-preset-react-app from babel-preset-latest to babel-preset-env. We should target ie 9.

We now have this beautiful warning:

warning react-scripts > babel-preset-react-app > babel-preset-latest@6.22.0:
💥  preset-latest accomplishes the same task as babel-preset-env.
🙏  Please install it with 'npm install babel-preset-env --save-dev'.
'{ "presets": ["latest" }'
 to 
'{ "presets": ["env"] }'.

For more info, please check the docs: http://babeljs.io/docs/plugins/preset-env 👌.
And let us know how you're liking Babel at @babeljs on 🐦

A PR doing this would be welcome, but please research the stability, too!