Automate Hathitrust Check

This PR includes:

code to trigger the hathitrust check right after import is done, removing the need to manually click the hathitrust 'check' button
unit tests of the new methods

For in-depth explanation of how this was tested in local/development environment, please see my comment here

Summary of changes:

inside the import_async(task) method in app/models/record_source.rb, instantiates a new hathitrust object, which then has the task passed through the hathitrust object's check_async() method
requires path to Hathitrust model inside the Task model
inside Task model, includes a new callback (after_save) that first checks if the import is completed before triggering the hathitrust check
inside Task model, adds two new methods:
1. import_task_completed? which includes logic for checking the statusand service of the task. If the environment is in prod/demo, the status it looks for is SUCCEEDED. The service it looks for is LOCAL STORAGE.
2. triggers_hathitrust_check(task), which instantiates a new hathitrust object, creates a new task (with service equal to Hathitrustand service equal to SUBMITTED), and passes that newly created task inside the check_async()method. In prod/demo this should trigger the hathitrust check process; in development, some tweaking will be required, such as calling on the check()method and commenting out the Book.analyze_table method inside the Hathitrust model.
This tweak should ONLY be done to see how this works in development, and should not be in the production code.
inside app/views/tasks/_tasks.html.haml, the button to run the Hathitrust check is removed completely, and the alert notice at the top points to this change:

adds several new tests inside test/models/task_test.rb, which looks at how a Task object is created upon default, and how the new methods affect those attributes. All tests pass, and existing tests don't break with the new changes:

medusa-project / book-tracker