asynchronous refactoring

- don't execute celery tasks directly
- introduce optional parameters to fileserver tasks to allow chaining
- handle user/group/key create and delete tasks in new osusers.signals
  class
- adapt unit tests
- change TaskResults model to store the task signatures
- generalize the local settings' logging configuration

gnuviechadmin/taskresults/migrations/0002_auto_20151011_2248.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('taskresults', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='taskresult',
+            name='task_name',
+        ),
+        migrations.AddField(
+            model_name='taskresult',
+            name='creator',
+            field=models.TextField(default='migrated', verbose_name='Task creator'),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='taskresult',
+            name='notes',
+            field=models.TextField(default='', verbose_name='Task notes'),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='taskresult',
+            name='signature',
+            field=models.TextField(default='', verbose_name='Task signature'),
+            preserve_default=False,
+        ),
+    ]