Initial implementation of integrated hubot.

Script loading isn't quite settled yet; I've only brought over the
`ping` script for now.  The `codex` script will have to be reworked to
use direct `Meteor.call` invocations; there might also be some
`Meteor.bindEnvironment` required (but maybe not).

Change-Id: I04c5d7a350bc5bb67a0e561914a5653215ab25b9