Revamp CSS Modules implementation to use .module.css filename convention

[swernerx]

To improve interoperability with 3rd party JS and CSS libraries it seems to be a good idea to follow the .module.css filename convention for enabling CSS modules. For all "normal" CSS files we won't use CSS modules anymore. This improves compatibility with React components which follow a strict CSS naming convention and aligns with tools like Create React App and Razzle.

See also: https://github.com/facebookincubator/create-react-app/pull/2285/files

[swernerx]

We have to keep in mind that our very own prepublish tool is not generating .module.css filenames right now but instead just use hashes. We have to add an option there to keep to toggle whether CSS files are module files... maybe there could be also some auto-detection e.g. when original file name contains .module.css then we use the same "extension" on the output file.

[swernerx]

Razzle uses this feature description: "Comes with the same CSS setup as create-react-app" - maybe good to copy it for our readme.