Use external Twitter config module

:warning: **WIP** :warning: 

Created new external module (https://github.com/afeld/hubot-twitter-config) to make require-ing Twitter config from scripts in this repo and from private Hubot instances easier.  Includes commits and lessons learned from #1179.

* [ ] Update dependency notes in scripts
* [ ] Update README to point to https://github.com/afeld/hubot-twitter-config

/cc @jlord @technicalpickles