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/twitter/twitter-bot

@@ -66,8 +66,7 @@ Make sure to go the application you created and click "create my
 access token" as well. Fill in the values displayed.
 """
 
-def write_config(config, configfile_path):
-    # type: (ConfigParser, str) -> None
+def write_config(config: ConfigParser, configfile_path: str) -> None:
     with open(configfile_path, 'w') as configfile:
         config.write(configfile)