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/i18n.py

@@ -1,16 +1,15 @@
+import logging
 import operator
+import os
+from itertools import zip_longest
+from typing import Any, Dict, List
 
+import ujson
 from django.conf import settings
 from django.utils import translation
-from django.utils.translation import ugettext as _
 from django.utils.lru_cache import lru_cache
+from django.utils.translation import ugettext as _
 
-from itertools import zip_longest
-from typing import Any, List, Dict
-
-import os
-import ujson
-import logging
 
 def with_language(string: str, language: str) -> str:
     """