Sets non-interaction flag for scroll analytics events

Before, ScrollTo events were not being flagged as non-interaction events,
so google was factoring them into bounce rates. This flags ScrollTo events
as non-interactive to fix this.

Info on non-interactive flag:
https://developers.google.com/analytics/devguides/collection/gajs/eventTrackerGuide#non-interaction
Merge pull request #425 from alphagov/non-interaction-flag-for-scroll-tracking

Sets non-interaction flag for scroll analytics events
Adding /government/world to scroll depth tracking
Merge pull request #427 from zilnhoj/patch-1

Related to Pivotal ticket https://www.pivotaltracker.com/story/show/70428922

This turns on scroll tracking for /government/world