add async example tests (for #1481)

[fshowalter]

This adds specs for the async example. It required a few changes:

• actions
  • isomorphic-fetch changed to be called via it's global in order to mock it with fetch-mock
• App.js
  • changed to export the un-connected component for test.
  • changed to pass it's action creators via props in order to mock them in the specs.
  • changed to fetch in componentWillMount instead of componentDidMount to test via shallow-rendering. This keeps with React's advice about when to fetch data, so win-win.

[timdorr]

This will need to be rewritten because of #1883. Please resubmit!