Adds StatHat logging

Adds StatHat logging to:
- general consuming of the CSV import file: `consumeCSVImport`
- creation of new Drupal user: `createDrupalUser`
  - track existing Drupal user account: `Existing DrupalUser`
- log when the transaction is distributed to other queues / consumers: `Distribute user import - user.registration.transactional`
- log when new user is sent the temporary Drupal user password email: `Sent user_password-niche`
- log when an existing Mailchimp account is found for the email: `Mailchimp - existing account`
- log when an existing Mobile Commons account is found for the phone number: `Mobile Commons - existing account`
If the above two stats are errors, should it even be allowed to get to this point? Wondering if this `clearAddedStatNames()` is actually not necessary and we should instead be returning out of this function when the errors are reached.