Sets non-interaction flag for scroll analytics events

Story: https://www.pivotaltracker.com/story/show/73607116

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