refactor(ServerRendering) simpler server rendering assets

[rmosolgo]

We have a problem with Sprockets 3.

• We add lib/assets/react-source/{ production | development } to the asset pipeline
• This makes it so //= require react works for production build or development build
• For some reason, Sprockets 3 puts those files in the manifest as production/react-server instead of react-server (Server-side rendering is not working with sprockets-rails 3.0 #443 (comment))
• As a result, we can't find the file from the manifest. (The logical_path has changed!)

Why does it do that?! I don't know. But I think this is a chance to simplify the default server rendering setup.

Right now, we require ["react-server.js", "components.js"]. Because react-server is "automatic", it's a bit hidden. I think we should add a new file called server_rendering.js which includes those two files. This is good because:

• By default, you have total control over the SSR manifest
• Less "automatic" stuff that can just break and stop you from building a sweet app
• react-server.js becomes a public API (I'm using this for my app already, I need renderToString)

However, this introduces some breaking changes:

• To upgrade, you should add the server_rendering.js manifest

TODO:

• Why are the compiled assets different?

[franzejr]

I agree README is not totally friendly related to the react-server file.

[caseys]

"automatic" react-server.js has been confusing for me too.