Manipulate chat handles via chat

[christophermaier]

Cogctl has:

• cogctl chat-handles - list everything
• cogctl chat-handles create <user> <handle> <provider> - associate a handle with a user
• cogctl chat-handles delete <user> <provider> - dissociate a handle from a user

For chat, we can do:

• operable:user create-handle <cog_username> <chat_handle> - associate the handle with the user for the current chat provider
• operable:user delete-handle <cog_username> - dissociate the handle from the user for the current chat provider

(Maybe use different terminology? link-handle? associate-handle? attach-handle?)

Seems like having this reside under the user command makes more sense than having a separate top-level command... this is probably what we should have done with cogctl to begin with.

We could add a "list handles" command as well, but with some refinements to the table command the same thing could be done with a pipeline based on operable:user list.

[christophermaier]

Slight tweak: we're going to go ahead and add a simple operable:user list-handles command