Add StateHandler to contrib_bots/run.py.

This allows bots to be stateful.  It doesn't handle persistence
after the bot shuts down, but it does store state between
invocations of handle_message.

contrib_bots/lib/help.py

@@ -23,7 +23,7 @@ class HelpHandler(object):
 
         return True
 
-    def handle_message(self, message, client):
+    def handle_message(self, message, client, state_handler):
         help_content = '''
             Info on Zulip can be found here:
             https://github.com/zulip/zulip