adds pluggable brokers

* added redis broker
 * added django_redis broker
 * added task acknowledgement

django_q/tests/test_config.py

@@ -3,11 +3,6 @@ import pytest
 from django_q import conf
 
 
-@pytest.fixture
-def r():
-    return conf.redis_client
-
-
 def test_django_redis():
     conf.Conf.DJANGO_REDIS = None
     assert conf.redis_client.ping() is True