Clean up all imports

* Use relative imports within djrill package
* Standardize ordering
* Remove absolute_import (it's standard in all
  python versions we now support)

djrill/tests/test_mandrill_webhook.py

@@ -1,7 +1,7 @@
-from base64 import b64encode
 import hashlib
 import hmac
 import json
+from base64 import b64encode
 
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured