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_bots/zulip_bots/test_file_utils.py

@@ -15,8 +15,7 @@ directory structure is currently:
             fixtures/
 '''
 
-def get_bot_message_handler(bot_name):
-    # type: (str) -> Any
+def get_bot_message_handler(bot_name: str) -> Any:
     # message_handler is of type 'Any', since it can contain any bot's
     # handler class. Eventually, we want bot's handler classes to
     # inherit from a common prototype specifying the handle_message
@@ -24,8 +23,7 @@ def get_bot_message_handler(bot_name):
     lib_module = import_module('zulip_bots.bots.{bot}.{bot}'.format(bot=bot_name))  # type: Any
     return lib_module.handler_class()
 
-def read_bot_fixture_data(bot_name, test_name):
-    # type: (str, str) -> Dict[str, Any]
+def read_bot_fixture_data(bot_name: str, test_name: str) -> Dict[str, Any]:
     base_path = os.path.realpath(os.path.join(os.path.dirname(
         os.path.abspath(__file__)), 'bots', bot_name, 'fixtures'))
     http_data_path = os.path.join(base_path, '{}.json'.format(test_name))