Comeback Clothes SMS - H&M Employee Engagement

* New module for Comeback Clothes
* With a new endpoint to receive the tips from `comeback-clothes/poster-tips`
* `config.json` defines what tips are getting delivered
* A LOT of the stuff in comebackclothes-api.js is copied and pasted from babysitter-api.js. It works for now, but there'll be a new issue created to figure out a better way to handle adding tip flows.

Closes #13