Multiple queue, multiple cluster in one site (#71)

* Support for multi-queue, multi-cluster configuration. API changes include:
  * Adding `cluster` to async_task() parameters and Task model
  * Adding argument --name to qcluster command
  * Necessary adjustments to Conf and Broker classes
  * Some admin improvements

* Add settings.Q_CLUSTER['ALT_CLUSTERS']: q_cluster config overrides for alternative clusters;
Add Conf.CLUSTER_NAME: separate usage from Conf.PREFIX;
QueueAdmin/OrmQ detail page enhanced: now displaying args/kwargs/q_options instead of encrypted payload.

* if `cluster` argument is not set (the default), async_task() and schedule() will be handled by the default cluster; Documentation update.

* Text cleanup

* Documentation update.

* Fix TIMEOUT setting in Windows for non-default cluster

---------

Co-authored-by: Stan Triepels <1939656+GDay@users.noreply.github.com>

django_q/brokers/redis_broker.py

@@ -11,7 +11,8 @@ except ImportError:
 
 
 class Redis(Broker):
-    def __init__(self, list_key: str = Conf.PREFIX):
+    def __init__(self, list_key: str = None):
+        list_key = list_key or Conf.CLUSTER_NAME
         super(Redis, self).__init__(list_key=f"django_q:{list_key}:q")
 
     def enqueue(self, task):
@@ -57,7 +58,7 @@ class Redis(Broker):
             return self.connection.mget(keys)
 
     @staticmethod
-    def get_connection(list_key: str = Conf.PREFIX) -> Redis:
+    def get_connection(list_key: str = None) -> Redis:
         if django_redis and Conf.DJANGO_REDIS:
             return django_redis.get_redis_connection(Conf.DJANGO_REDIS)
         if isinstance(Conf.REDIS, str):