Remove MAS-specific styles

This PR removes all styles that are relevant only to the MAS brand and that are non-generic. The styles have been moved into [frontend/add-dough-styles](https://github.com/moneyadviceservice/frontend/compare/add-dough-styles), and for the shared helpers (such as how MAS itself deals with media queries) have been created as a bower component called [Yeast](https://github.com/moneyadviceservice/yeast).

Frontend now uses a 'theme' layer to make the Dough components look like MAS.

The version number has been bumped as this is a breaking change.
:boom: