Renzo/instrument verified cert flow

This PR adds tracking instrumentation to the verified cert flow. It might be useful to add events to this flow later, but for the time being, these pageload tracking calls will allow us to surface the full funnel in Mixpanel. Please note that I've only instrumented those transitions which Segment.io isn't already picking up as a result of the URL changing.

@shnayder and @dianakhuang, could you please review this?