As part of the migration away from AngularJS, replace Angulartics with
direct usage of the Google Analytics client.

Since we only use a single analytics provider (Google Analytics) and
only basic event tracking functionality in a single-route application,
its easiest just to replace the code with direct calls to the
analytics.js API.

See https://developers.google.com/analytics/devguides/collection/analyticsjs/events

Fixes #976