Usage of setState with unmounted component

**view.js**
```es6
class View extends Component {

//...

addGroup() {
this.props.addGroup({ name: 'Name of Group' }).then(({data}) => {
this.setState((prevState) => ({
addedGroups: [...prevState.addedGroupd, data]
}))
})
}

//...
```

If the component unmounts before the request finish, you will get the
`Warning: Can't call setState (or forceUpdate) on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.` warning. Do you have a solution for this?

Start with view.js and the addGroup method shown in the issue, then inspect how the request promise and component lifecycle are handled. Reproduce the unmount-before-completion case and confirm that the completed request no longer attempts state updates after unmounting.

Written by the indexing model from the issue text.