V2 theme refactor

Most notable changes:

- Deprecate color use cases
- Add anchors to demos for better testing
- Rewrite button generation pattern /cc @AlbertoElias there's less magic happening in there. Let me know what you think!

This PR also fixes many visual regressions introduced in the previous merge.

Idea for a next step: improve demos to cover more cases (elements, [backgrounds](http://jsbin.com/gezize/1/edit?html,output))
@danskinner As for your last paragraph, that's a given and that's why I was seeing the risk of not forcing a font as really low.

We have decided to add the font in the module, and for now, not allowing you to change it from the module, though you can always do it anyway via CSS.