Storymap13 header and responsiveness

Fixing

* https://github.com/geoadmin/web-storymaps/issues/118, https://github.com/geoadmin/web-storymaps/issues/119 Links
* https://github.com/geoadmin/web-storymaps/issues/120 (works only with the official address. I do not want technical addresses to be tweeted)
* https://github.com/geoadmin/web-storymaps/issues/121 New CMS 2014 light CSS
* https://github.com/geoadmin/web-storymaps/issues/122 Responsiveness
* https://github.com/geoadmin/web-storymaps/issues/123