CLC-3909: Selenium test for Google tasks

The purpose of the test is to verify the UI behavior for managing Google tasks in the dashboard "To Do" card.  
Since the Selenium code required for the To Do card is extensive, I've moved it into its own class and converted the My Dashboard page to a module.  Having classes representing individual cards rather than entire pages seems like a good strategy going forward, as it improves readability and maintainability.

The test user is new, and its credentials will need to be added to config in order for the tests to run successfully.  Note that there are no explicit tests for deleting tasks, since every test deletes all existing tasks before performing its specific actions.