typing: Convert function type annotations to Python 3 style.

Generated by com2ann (slightly patched to avoid also converting
assignment type annotations, which require Python 3.6), followed by
some manual whitespace adjustment, and two fixes for use-before-define
issues:

-    def set_zulip_client(self, zulipToJabberClient: ZulipToJabberBot) -> None:
+    def set_zulip_client(self, zulipToJabberClient: 'ZulipToJabberBot') -> None:

-def init_from_options(options: Any, client: Optional[str] = None) -> Client:
+def init_from_options(options: Any, client: Optional[str] = None) -> 'Client':

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

zulip/integrations/perforce/zulip_perforce_config.py

@@ -28,8 +28,7 @@ P4_WEB = None
 # "master-plan" and "secret" subdirectories of //depot/ to:
 # * stream "depot_subdirectory-commits"
 # * subject "change_root"
-def commit_notice_destination(path, changelist):
-    # type: (Text, int) -> Optional[Dict[Text, Text]]
+def commit_notice_destination(path: Text, changelist: int) -> Optional[Dict[Text, Text]]:
     dirs = path.split('/')
     if len(dirs) >= 4 and dirs[3] not in ("*", "..."):
         directory = dirs[3]