Save worker information to database for persistence across runs and abstract away data source

lib/render_workers/render_worker.py

@@ -242,6 +242,8 @@ class BaseRenderWorker(object):
 
     def json(self):
         worker_data = self.__dict__.copy()
+        worker_data['percent_complete'] = self.percent_complete()
+        worker_data['time_elapsed'] = self.time_elapsed()
         keys_to_remove = ['thread', 'process']  # remove unwanted keys from dict
         for key in worker_data.keys():
             if key.startswith('_'):