Add management command to purge periodic tasks from the DB.

mayan/apps/common/management/commands/purgeperiodictasks.py

@@ -0,0 +1,12 @@
+from __future__ import unicode_literals
+
+from django.core import management
+
+from djcelery.models import PeriodicTask
+
+
+class Command(management.BaseCommand):
+    help = 'Removes all periodic tasks.'
+
+    def handle(self, *args, **options):
+        PeriodicTask.objects.all().delete()