Issue 3197 user skin ui

https://code.google.com/p/otwarchive/issues/detail?id=3197
Better toggling between Site and Work skins so you know where you are. Rebased on current master and corresponding tests updated to pass. (The UI code was originally submitted as https://github.com/otwcode/otwarchive/pull/782 but I couldn't get the branch to rebase properly)