Add custom SharedCounter / Queue

This will not fix anything related to Django 2.0 but will allow MAC
users to run Django-Q allowing tests to be run locally.

django_q/conf.py

@@ -1,7 +1,7 @@
 import logging
 from copy import deepcopy
 from signal import signal
-from multiprocessing import cpu_count, Queue
+from multiprocessing import cpu_count
 
 # django
 from django.utils.translation import ugettext_lazy as _
@@ -11,6 +11,9 @@ from django.conf import settings
 import os
 import pkg_resources
 
+# local
+from django_q.queues import Queue
+
 # optional
 try:
     import psutil