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
This omission meant that this whole test wasn't running which is somewhat alarming since CI didn't report a problem. It seems that the jasmine CI run simply ignores test files with syntax errors rather than failing. Perhaps linting the script as part of the run will fix this, but that's something for a different PR.