adds pluggable brokers

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

django_q/brokers/django_redis.py

@@ -0,0 +1,10 @@
+import django_redis
+from django_q.brokers import redis
+from django_q.conf import Conf
+
+
+class DjangoRedis(redis.Redis):
+
+    @staticmethod
+    def get_connection():
+        return django_redis.get_redis_connection(Conf.DJANGO_REDIS)