demo portions of documentation are missing/404

[frostius]

The demo portions of www.polymer-project.org documentation are missing/404. Specifically the [icons](https://www.polymer-project.org/components/core-icons/demo.html], core-elements and paper-elements demo pages.

[ebidel]

Please see https://blog.polymer-project.org/updates/2015/03/10/updated-site/