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

docs/resource_copy.md

@@ -102,7 +102,7 @@ available fields.
 ```
 
 `CopyAPIView` will automatically detect sub objects of an object, and do a deep copy of all sub objects
-as a background celery task. There are sometimes permission issues with sub object copy. For example,
+as a background task. There are sometimes permission issues with sub object copy. For example,
 when copying nodes of a workflow job template, there are cases where the user performing copy has no use
 permission of related credential and inventory of some nodes, and it is desired those fields will be
 `None`. In order to do that, developer should provide a static method `deep_copy_permission_check_func`