Support .css files

[jurassix]

create-react-app bootstraps css support loaded from JavaScript; JS files have import statements to .css files. We need to update our JS files if these move.

[PatricSachse]

Does this prefer to (I would call it) bug that each import of a css-file is destroyed after moving files by removing the .css ending in the import? We're using postCss and it is actually a little tricky to use your plugin because of this behaviour :/