Adds tools for CSS minifying.

Hi!

What a cool button project, really nice. Great work.

I've added CSS minifying tools for project developers. It's a `make`-based setup that installs LessCSS using `npm`.

Also there's a target `make all` that minifies the source CSS file. If you feel like adding it to the repository you should simply be able to run the make target and then commit the minified CSS-file. Since the original is pretty sleek, it doesn't save that many bytes, but who knows, it might be nice to have.

I hope you find this useful.

Cheers!
/O