Hubot ignores itself and manages own channel subscriptions

This PR contains various significant refactoring including:

 * reply to channel that request was made in rather than always to the primary channel (id=1)
 * subscribe automatically to all channels (obsoleting HUBOT_KANDAN_CHANNELS parameter)
 * better error handling
 * ignore messages from ourselves by knowing who ourself is
 * subscribe to new channels that are created, unsubscribe from channels that are destroyed

This instance of the Hubot Kandan adapter requires a number of modifications to Kandan itself, covered in separate pull requests, and will [a] only work against master and [b] is not guaranteed to work until those PRs are merged. :wink: