Add notifyOnNetworkStatusChange

Waiting on: https://github.com/apollographql/react-apollo/issues/2324

Branch `8`, after `Now we’ve got login working.`

```js
export const withUser = graphql(USER_QUERY, {
  options: { notifyOnNetworkStatusChange: true },
  props: ({ data: { currentUser, loading } }) => ({
    user: currentUser,
    loggingIn: loading
  })
})
```