Add celery task for get_email

Allows you to get_email even without cron, thus enabling the use of django-helpdesk of cronless PaaS services.

helpdesk/tasks.py

@@ -0,0 +1,8 @@
+from celery import task
+
+from .email import process_email
+
+
+@task()
+def helpdesk_process_email():
+    process_email()