Add civicrm_handler_field_contact_image to Views implementation

Currently the image_url field is handled as a string in Drupal Views, which of course it is. However the most likely use case when this field is used in Views is to display the image. Drupal core provides server side image styling. Contrib contains the powerful Picture module for responsive images. civicrm_handler_field_contact_image enables Picture module integration if enabled and falls back to core image styling