Initialise clients outside the app

This avoids the annoying problem where you can’t import a client unless
the app has already been initialised.

app/notify_client/events_api_client.py

@@ -12,3 +12,6 @@ class EventsApiClient(NotifyAdminAPIClient):
         }
         resp = self.post(url='/events', data=data)
         return resp['data']
+
+
+events_api_client = EventsApiClient()