GA: added non-interaction parameter based on options

@harrietgrace @calvinfo 

We're adding an advanced option in the GA integration to allow our customers to choose whether to mark all track events as non-interactive or not. Events are by default 'interactive', meaning they count as an interaction with the website, and do no count towards bounce rate (people who view your website, and then leave without interacting / everyone who visits your page). Our customers will still have the ability to override this setting with individual event calls, if they wish to.

Fixes https://segment.zendesk.com/agent/#/tickets/17523


99% sure this won't matter, but probably still safe to make sure this becomes a boolean by doing `!!nonInteraction`. their docs leave a little bit to be desired there :(

https://developers.google.com/analytics/devguides/collection/gajs/eventTrackerGuide