Google Analytics

If gaPropertyId is defined in application settings, load ga.js script.
About page for liftie
Include /about link in the sitemap
Client side of about component

If a Liftie page is displayed for the first time, we show About section and
install 'click' handler for the close button.
'resorts-open' cookie is used to determine if this is the first time
Liftie is used.
Merge branch 'analytics'
Merge branch 'about'
Release 1.9.0