replace celery task decorators with a kombu-based publisher

this commit implements the bulk of `awx-manage run_dispatcher`, a new
command that binds to RabbitMQ via kombu and balances messages across
a pool of workers that are similar to celeryd workers in spirit.
Specifically, this includes:

- a new decorator, `awx.main.dispatch.task`, which can be used to
  decorate functions or classes so that they can be designated as
  "Tasks"
- support for fanout/broadcast tasks (at this point in time, only
  `conf.Setting` memcached flushes use this functionality)
- support for job reaping
- support for success/failure hooks for job runs (i.e.,
  `handle_work_success` and `handle_work_error`)
- support for auto scaling worker pool that scale processes up and down
  on demand
- minimal support for RPC, such as status checks and pool recycle/reload

tools/docker-compose/Procfile

@@ -1,8 +1,7 @@
 nginx:          make nginx
 runworker:      make runworker
 daphne:         make daphne
-celeryd:        make celeryd
+dispatcher:     make dispatcher
 receiver:       make receiver
-flower:         make flower
 uwsgi:          make uwsgi
-jupyter:        make jupyter
+jupyter:        make jupyter