Refactor: DistributedJobManager with pub/sub status change notifications (#25)

* Add pubsub to render_queue and base_worker

* Refactor: Convert ZeroconfServer to Singleton with Class Methods

* New API for subjob servers to notify parent job servers of status changes

* Refactor: Move all subjob related methods to distributed_job_manager.py

* Rewrite for wait_for_subjobs

* Fix: DistributedJobManager.find_available_servers() takes 1 positional argument but 3 were given

* DistributedJobManager should now notify / be notified abotu background job changes

* Fix the make_ready api. Change children keyname to be id@hostname so it can be unique

* Fixes

* Image sequence to movie needs to find the actual start frame

* Fix: subjob_status_change did not return a valid response

* Fix client renderer selection

* Small fix for subjob status checking

* Fix issue with divide_frames_equally

* Fix issue where downloads were not occurring

* Fix issue where old status was being reported

* Add docstrings and code cleanup

lib/client/new_job_window.py

@@ -175,9 +175,8 @@ class NewJobWindow(Frame):
         self.presets = self.server_proxy.request_data('presets', timeout=3) or {}
 
         # update available renders
-        available_renderers = [x for x in self.renderer_info.keys() if self.renderer_info[x].get('available', False)]
-        self.renderer_combo['values'] = available_renderers
-        if available_renderers:
+        self.renderer_combo['values'] = list(self.renderer_info.keys())
+        if self.renderer_info.keys():
             self.renderer_combo.current(0)
 
         self.refresh_renderer_settings()