Warning: forceUpdate(...): Can only update a mounting component

[louy]

With server-side rendering, I'm getting this warning a lot:

Warning: forceUpdate(...): Can only update a mounting component. This usually means you called forceUpdate() outside componentWillMount() on the server. This is a no-op. Please check the code for the LoginPage component.

I think the issue is that observer starts listening for changes on componentWillMount and stops on componentWillUnmount. However, react-dom/server never calls componentWillUnmount as the component is never mounted in the first place.

I'm not sure how to solve this to be honest, but the way it works right now probably has a lot of memory leaks as well.

[mweststrate]

See #140, a feature will soon be added to stop subscribing to data changes on the server.