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/management/commands/qcluster.py

@@ -2,6 +2,7 @@ from django.core.management.base import BaseCommand
 from django.utils.translation import gettext as _
 
 from django_q.cluster import Cluster
+import os
 
 
 class Command(BaseCommand):
@@ -16,8 +17,21 @@ class Command(BaseCommand):
             default=False,
             help="Run once and then stop.",
         )
+        parser.add_argument(
+            "-n",
+            "--name",
+            dest="cluster_name",
+            default=None,
+            help="Set alternative cluster name instead of the name in Q_CLUSTER settings (for multi-queue setup). "
+                 "On Linux you should set name through `Q_CLUSTER_NAME=cluster_name python manage.py qcluster` instead."
+        )
 
     def handle(self, *args, **options):
+        # Set alternative cluster_name before creating the cluster (cluster_name is broker's queue_name, too)
+        cluster_name = options.get("cluster_name")
+        if cluster_name:
+            os.environ["Q_CLUSTER_NAME"] = cluster_name
+
         q = Cluster()
         q.start()
         if options.get("run_once", False):