feat(button): wrapping and spaced variant

This PR adds new button group variants wrapping and spaced
There also exists another optional wrapped helper class which should be set when it's known if a button group is actually wrapped (this will adjust some border-radius values). It is not possible to detect a wrapping child automatically via pure CSS, that's why the developer should handle this using that helper class whenever needed.

The PR also fixes some adjustments when used together with basic and/or inverted and improved conditional compilation at some places

Author: lubber-de