zulip_bots: Make StateHandler optional.

This has the convenient side-effect of making
the bot_handler.storage attribute read-only.

zulip_bots/zulip_bots/bots/incrementor/incrementor.py

@@ -2,6 +2,11 @@
 
 
 class IncrementorHandler(object):
+    META = {
+        'name': 'Incrementor',
+        'description': 'Example bot to test the update_message() function.',
+        'uses_storage': True,
+    }
 
     def usage(self):
         return '''

zulip_bots/zulip_bots/bots/tictactoe/tictactoe.py

@@ -267,6 +267,11 @@ class ticTacToeHandler(object):
     tic-tac-toe bot! Make sure your message starts with
     "@mention-bot".
     '''
+    META = {
+        'name': 'TicTacToe',
+        'description': 'Lets you play Tic-tac-toe against a computer.',
+        'uses_storage': True,
+    }
 
     def usage(self):
         return '''

zulip_bots/zulip_bots/bots/virtual_fs/virtual_fs.py

@@ -4,6 +4,12 @@ import re
 import os
 
 class VirtualFsHandler(object):
+    META = {
+        'name': 'VirtualFs',
+        'description': 'Provides a simple, permanent file system to store and retrieve strings.',
+        'uses_storage': True,
+    }
+
     def usage(self):
         return get_help()