Move Spree::StaticPage and Spree:StaticRoot to facilitate overrides with decorator

Hi, we are working on a gem that enable static page localization. We need to override this two classes, but we are not able if they lives in routes.rb. 
Out gem link is [https://github.com/geekcups-team/spree_static_content_i18n](https://github.com/geekcups-team/spree_static_content_i18n)