Set GA custom var scope to the same as wikiamobile skin

All the custom vars in https://github.com/Wikia/app/blob/dev/extensions/wikia/AnalyticsEngine/js/analytics_prod.js#L136 are set to level 3 (pageview) scoping in GA. We should be set to the same in order for the most accurate comparison.

@tedgill @mklucsarits