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/views/upload.py

@@ -1,17 +1,24 @@
-from django.http import HttpRequest, HttpResponse, HttpResponseForbidden, \
-    HttpResponseNotFound
+from mimetypes import guess_type
+
+from django.conf import settings
+from django.http import HttpRequest, HttpResponse, HttpResponseForbidden, HttpResponseNotFound
 from django.shortcuts import redirect
 from django.utils.cache import patch_cache_control
 from django.utils.translation import ugettext as _
-
-from zerver.lib.response import json_success, json_error
-from zerver.lib.upload import upload_message_image_from_request, get_local_file_path, \
-    get_signed_upload_url, check_upload_within_quota, INLINE_MIME_TYPES, \
-    generate_unauthed_file_access_url, get_local_file_path_id_from_token
-from zerver.models import UserProfile, validate_attachment_request
-from django.conf import settings
 from django_sendfile import sendfile
-from mimetypes import guess_type
+
+from zerver.lib.response import json_error, json_success
+from zerver.lib.upload import (
+    INLINE_MIME_TYPES,
+    check_upload_within_quota,
+    generate_unauthed_file_access_url,
+    get_local_file_path,
+    get_local_file_path_id_from_token,
+    get_signed_upload_url,
+    upload_message_image_from_request,
+)
+from zerver.models import UserProfile, validate_attachment_request
+
 
 def serve_s3(request: HttpRequest, url_path: str, url_only: bool) -> HttpResponse:
     url = get_signed_upload_url(url_path)