[core] Added ApplicationStartedEvent to Redis bus instead of application.

The Redis bus now uses a pub/sub architecture rather than a simple
queue.

Earlier on, the application could post an event to the queue and then
pick it up when it started listening.

When doing a publish on a pub/sub channel, however, any messages
sent before the client started listening will be lost.

platypush/app/_app.py

@@ -19,7 +19,6 @@ from platypush.entities import init_entities_engine, EntitiesEngine
 from platypush.event.processor import EventProcessor
 from platypush.logger import Logger
 from platypush.message.event import Event
-from platypush.message.event.application import ApplicationStartedEvent
 from platypush.message.request import Request
 from platypush.message.response import Response
 from platypush.utils import get_enabled_plugins, get_redis_conf
@@ -462,7 +461,6 @@ class Application:
             self.cron_scheduler.start()
 
         assert self.bus, 'The bus is not running'
-        self.bus.post(ApplicationStartedEvent())
 
         # Poll for messages on the bus
         try:

platypush/bus/redis.py

@@ -37,8 +37,12 @@ class RedisBus(Bus):
         """
         Polls the Redis queue for new messages
         """
+        from platypush.message.event.application import ApplicationStartedEvent
+
         with self.pubsub as pubsub:
             pubsub.subscribe(self.redis_queue)
+            self.post(ApplicationStartedEvent())
+
             try:
                 for msg in pubsub.listen():
                     if msg.get('type') != 'message':