CLC-4065: Selenium test for Live Updates

Adds a new test to verify live updates of Google mail and calendar tasks.  The test also verifies the revoking and requesting of Google OAuth tokens, including the content of the Google authorization page.  The test will await the live update button for the configured Google mail cache expiration plus 180 seconds.

This PR also includes refactoring affecting the other Google tasks test, such as changing MyDashboardPage from a module to a class.
You should definitely make the "180" a configurable param -- something like Settings.ui_selenium.live_update_timeout_delta.