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/lib/push_notifications.py

@@ -1,32 +1,37 @@
 import base64
 import binascii
 import logging
-import lxml.html
 import re
 import time
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple, Union
 
-from typing import Any, Dict, List, Optional, Tuple, TYPE_CHECKING, Union
-
+import gcm
+import lxml.html
+import ujson
 from django.conf import settings
 from django.db import IntegrityError, transaction
 from django.db.models import F
 from django.utils.timezone import now as timezone_now
 from django.utils.translation import ugettext as _
-import gcm
-import ujson
 
 from zerver.decorator import statsd_increment
 from zerver.lib.avatar import absolute_avatar_url
 from zerver.lib.exceptions import JsonableError
-from zerver.lib.message import access_message, \
-    bulk_access_messages_expect_usermessage, huddle_users
-from zerver.lib.remote_server import send_to_push_bouncer, send_json_to_push_bouncer
+from zerver.lib.message import access_message, bulk_access_messages_expect_usermessage, huddle_users
+from zerver.lib.remote_server import send_json_to_push_bouncer, send_to_push_bouncer
 from zerver.lib.timestamp import datetime_to_timestamp
-from zerver.models import PushDeviceToken, Message, Recipient, \
-    UserMessage, UserProfile, \
-    get_display_recipient, receives_offline_push_notifications, \
-    receives_online_notifications, get_user_profile_by_id, \
-    ArchivedMessage
+from zerver.models import (
+    ArchivedMessage,
+    Message,
+    PushDeviceToken,
+    Recipient,
+    UserMessage,
+    UserProfile,
+    get_display_recipient,
+    get_user_profile_by_id,
+    receives_offline_push_notifications,
+    receives_online_notifications,
+)
 
 if TYPE_CHECKING:
     from apns2.client import APNsClient