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`
The clear is more for the StatHat collection further in the code: 
```
$this->statHat->addStatName('Mobile Commons - existing account');
$this->statHat->reportCount(1);
```
The clear is to avoid adding another count to either `$this->statHat->addStatName('Mailchimp - existing account')` or `$this->statHat->addStatName('Mailchimp - error')`.