adds streamable feature to the library

[ImanMh]

Hi there. I've been working on this feature to make it possible to stream SSR react projects made with isomorphic-style-loader. Even though this is not backward compatible I sent you the initial modifications so that we can discuss on what I'm doing here. With this implementation the only change that you need to make to the code is this:

<StyleContext.Provider value={{ insertCss, css, isServer: true }}>
  <ClientRoot manifest={manifest} />
</StyleContext.Provider>

Users of this library must pass the CSS set and a flag that shows if this code is running on server or not (which can be detected by default if not provided but passing CSS set is mandatory). Before I go ahead and add tests for this feature let me know your thoughts. If you merge this we can have corresponding improvements on react-starter-kit as well.

[ImanMh]

this will fix #164

[ImanMh]

@frenzzy could you please check this out?

[frenzzy]

@ImanMh sorry, I am not interested in maintenance isomorphic-style-loader anymore since I switched to using Emotion (this feature is already there)

@koistya maybe deprecate this project in favor of something else or add a bold message to the readme about searching new maintainers?