Add mail template for failed celery tasks

aleksis/core/templates/templated_email/celery_failure.email

+{% load i18n %}
+
+{% block subject %}
+ {% blocktrans with task_name=task_name%} Celery task {{ task_name }} failed!{% endblocktrans %}
+{% endblock %}
+
+{% block plain %}
+ {% trans "Hello," %}
+ {% blocktrans with task_name=task_name %}
+   the celery task {{ task_name }} failed with following information:
+ {% endblocktrans %}
+
+
+{% blocktrans with task_name=task_name task=task task_id=task_id exception=exception args=args kwargs=kwargs traceback=traceback %}
+ * Task name: {{task_name}}
+ * Task: {{task}}
+ * Id of the task: {{task_id}}
+ * Exception instance raised: {{ exception }}
+ * Positional arguments the task was called with: {{ args }}
+ * Keyword arguments the task was called with: {{ kwargs }}
+ * Stack trace object: {{ traceback }}
+{% endblocktrans %}
+{% endblock %}
+
+{% block html %}
+ <p>{% trans "Hello," %}</p>
+ <p>
+  {% blocktrans with task_name=task_name %}
+    the celery task {{ task_name }} failed with following information:
+  {% endblocktrans %}
+ </p>
+
+ <ul>
+ {% blocktrans with task_name=task_name task=task task_id=task_id exception=exception args=args kwargs=kwargs traceback=traceback %}
+   <li>Task name: {{task_name}}</li>
+   <li>Task: {{task}}</li>
+   <li>Id of the task: {{task_id}}</li>
+   <li>Exception instance raised: {{ exception }}</li>
+   <li>Positional arguments the task was called with: {{ args }}</li>
+   <li>Keyword arguments the task was called with: {{ kwargs }}</li>
+   <li>Stack trace object: {{ traceback }}</li>
+ </ul>
+ {% endblocktrans %}
+{% endblock %}