New css loader plugin

Following of PR #213. Modification since last update of PR #213 is in this commit : https://github.com/clmath/delite/commit/1ff5c621f85ba125df715d1cd85f60f8e9a06341.

I see... it would probably be easier if you just renamed the local `require` variable to something else (like `req` or `moduleRequire`), so it didn't mask the global variable.