update research mode email callbacks to add process-ses-response task to queue

this involved:
* moving that task to callback_tasks to prevent circular imports
* updating the dummy research mode callbacks (with actual SNS messages from the
  ses simulator emails)
* refactoring tests

app/celery/callback_tasks.py

@@ -0,0 +1,18 @@
+from flask import current_app
+
+from app import notify_celery
+from app.config import QueueNames
+from app.statsd_decorators import statsd
+from app.notifications.notifications_ses_callback import process_ses_response
+
+
+@notify_celery.task(bind=True, name="process-ses-result", max_retries=5, default_retry_delay=300)
+@statsd(namespace="tasks")
+def process_ses_results(self, response):
+    try:
+        errors = process_ses_response(response)
+        if errors:
+            current_app.logger.error(errors)
+    except Exception:
+        current_app.logger.exception('Error processing SES results')
+        self.retry(queue=QueueNames.RETRY, exc="SES responses processed with error")