Add dynamic channel selector for Slack

Choose notified channel(room) by title of post on esa dynamically.
https://github.com/hmsk/hubot-esa#enable-channel-selector-for-slack

Use hubot-slack v4+ since this version

slack.attachment event handling is no longer supported by hubot-slack.
https://slackapi.github.io/hubot-slack/upgrading#upgrading-from-version-3-or-earlier

The decorator for Slack used to emitted slack.attachment.
Since this version, make messages through official way of Hubot such as robot.sendRoom, res.send.