Split verification dashboard analytics

This completes [ECOM-725](https://openedx.atlassian.net/browse/ECOM-725). Events are added to the dashboard to track interaction with upgrade copy, clicks on upgrade buttons, and clicks on "verify now" buttons. In addition to some refinement to the way events which track clicks on links are fired, the categories assigned to virtual pageviews generated during the payment and verification flows have been updated after a conversation with marketing.

@AlasdairSwan and @wedaly, could you review this when you're able?
I did some testing as you suggested. It doesn't look like elements added to the page after `trackLink` is executed in the `postRender` are tracked. Only those elements present on the page at the time `trackLink` is executed are tracked.

I initially tried using an `.on('click'...` approach to fire events, but the browser was redirected before events bound in this way could fire. `trackLink` is meant to solve this problem by inserting a small timeout which allows enough time for calls to Segment's `track` method to be made.

Since the elements of interest here are present on the page before `trackLink` is executed, and I've confirmed that the events fire after thorough testing, are you okay with keeping this as it is?