python: Sort imports with isort.

Fixes #2665.

Regenerated by tabbott with `lint --fix` after a rebase and change in
parameters.

Note from tabbott: In a few cases, this converts technical debt in the
form of unsorted imports into different technical debt in the form of
our largest files having very long, ugly import sequences at the
start.  I expect this change will increase pressure for us to split
those files, which isn't a bad thing.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/tornado/application.py

@@ -2,11 +2,12 @@ import atexit
 
 import tornado.web
 from django.conf import settings
-from zerver.tornado import autoreload
 
 from zerver.lib.queue import get_queue_client
+from zerver.tornado import autoreload
 from zerver.tornado.handlers import AsyncDjangoHandler
 
+
 def setup_tornado_rabbitmq() -> None:  # nocoverage
     # When tornado is shut down, disconnect cleanly from rabbitmq
     if settings.USING_RABBITMQ: