Drupal User to Contact Connector (Hook_User) and Domain ID Resolution

Implement hook_user functionality for CiviCRM. If module is enabled, then insert_user action will invoke insert_contact. On user update, we will check if contact exists for this user, and create one if needed.

Implement domain ID resolution - all UI and API functionality respects the domain ID which will be present in the session scope. Most of this can be taken care of by an addition to the code that builds the DAO files (genCode.php). Hand-coded queries (like Search) will need to be updated separately.

To facilitate user testing in our sandbox, we will assign a different domain ID to each user/tester (so they have their own data silo). This can happen manually.