Switcher for frontend experiments

If an experiment is available for an article (e.g. if the article was added to an event in the admin tool), it will be ajax'd into that article to replace the story-package/related articles.

The admin switchboard activates experiments. If more than one is activated, the first wins. Experiments must have routes starting "/experiment/..", e.g. 
/experiment/foobar01/the/page/id/etc

To bypass the switch mechanism, set a localStorage key of "gu.experiment" in your browser to the name of an experiment, e.g. "foobar01"

To add a new experiment, add a route/controller/view and a switch in the admin switchboard.  The switch's name must begin with "experiment", e.g. "experiment-foobar-01"