Implement a more dynamic celery queue system

* Meant to be a starting point to more efficiently manage work routing
  and to balance work across all tower nodes
* Integrate flower as a dev tool that starts alongside other nodes.
  Helpful for observing and monitoring the queues/exchanges
* For the moment, force the task manager to only run on one node (not
  sure if this is needed)
* Define queues and routes for all task work
* Bump celery version to 3.1.23
* Expose flower through haproxy

requirements/requirements_dev.txt

@@ -10,3 +10,4 @@ pytest-cov
 pytest-django
 pytest-pythonpath
 pytest-mock
+flower